scale.js

function scale(x, realMin, realMax, scaledMin, scaledMax) {
    var realDiff = realMax - realMin
    var scaledDiff = scaledMax - scaledMin
    var xOffset = x - realMin
    var ratio = xOffset / realDiff
    var appliedValue = ratio * scaledDiff
    var ret = scaledMin + appliedValue
    return ret
}   


var scaled = scale(75, 50, 100, 200, 300)
console.log(scaled)