https://www.freecodecamp.com/challenges/pairwise

desafios38.js

const array = [7, 9, 11, 13, 15]

const matchTwoNumbers = 20

const match = ( total, num, index, arr ) => {
	let sum = total + num 
	let indexs = []
	
	// console.log(total, num, sum, index, arr )
	
	if ( sum == matchTwoNumbers ) 
		indexs.push[ index ]	
    else 
    	//?

    return sum
}

const result = array.reduce( match, 0 )

console.log( result )