Tutorial available at: https://javascriptbible.wordpress.com/javascript-getting-started/javascript-basics/

CS5-script.js

//Create john family object
var johnFamily = {
    firstName: 'John',
    lastName: 'Smith',
    bills: [124, 48, 268, 180, 42], //all the bills values in an array
    calcTip: function() {
        
        this.tips = []; //new propety tips will be created
        this.totalPaid = []; //new property totalPaid will be ceated
        
        for(var i = 0; i < this.bills.length; i++) {
            
            var bill = this.bills[i]; //pick up the current value at index i
            var tip = 0; //tip variable will be initialized with 0 in every iteration
            
            if(bill < 50) {
                //20%
                tip = bill*(20/100) //20% tip calculation
            } else if(bill >= 50 && bill <= 200) {
                //15%
                tip = bill*(15/100)
            } else {
                //10%
                tip = bill*(10/100)
            }
            
            this.tips[i] = tip; //adding tip value to the tip poperty just created
            this.totalPaid[i] = bill+tip; //adding total value to totalPaid property
            
        } //End of for-loop
    } //End of CalcTip
};

//Creating mark's family object
var markFamily = {
    firstName: 'Mark',
    lastName: 'Smith',
    bills: [77, 375, 110, 45], //values updated with mark bills
    calcTip: function() {
        
        this.tips = [];
        this.totalPaid = [];
        
        for(var i = 0; i < this.bills.length; i++) {
            
            var bill = this.bills[i];
            var tip = 0;
            
            if(bill < 100) {
                //20%
                tip = bill*(20/100)
            } else if(bill >= 100 && bill <= 300) {
                //10%
                tip = bill*(10/100)
            } else {
                //25%
                tip = bill*(25/100)
            }
            
            this.tips[i] = tip;
            this.totalPaid[i] = bill+tip;
            
        } //End of for-loop
    } //End of CalcTip
};

//Function to calculate average of tips
function calcAvg(tips) {
    var sum = 0;
    for(var i = 0; i < tips.length; i++) {
        sum = sum + tips[i];
    }
    return sum/tips.length;
}

johnFamily.calcTip(); //calculating tips for john
markFamily.calcTip(); //calculating tips for mark
//console.log(johnFamily, markFamily);

johnFamily.avgTips = calcAvg(johnFamily.tips); //tips average for john getting stored in a new property avgTips
markFamily.avgTips = calcAvg(markFamily.tips); //tips averrage for mark getting stored in a new property avgTips

//Pringing the final result
if (johnFamily.avgTips > markFamily.avgTips) {
    console.log(johnFamily.firstName + '\'s family paid $' + johnFamily.avgTips + ' in tips which is more than what ' + markFamily.firstName + '\'s family pays i.e. $' + markFamily.avgTips);
} else if(johnFamily.avgTips < markFamily.avgTips) {
    console.log(markFamily.firstName + '\'s family paid $' + markFamily.avgTips + ' in tips which is more than what ' + johnFamily.firstName + '\'s family pays i.e. $' + johnFamily.avgTips);
} else {
    console.log(markFamily.firstName + '\'s family paid $' + markFamily.avgTips + ' in tips and ' + johnFamily.firstName + '\'s family pays i.e. $' + johnFamily.avgTips);
}