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JavaScript

var data = [{
    "Body Weight": 114,
    " Untrained": 80,
    " Novice": 145,
    " Intermediate": 175,
    " Advanced": 240,
    " Elite": 320
}, {
    "Body Weight": 123,
    " Untrained": 85,
    " Novice": 155,
    " Intermediate": 190,
    " Advanced": 260,
    " Elite": 345
}, {
    "Body Weight": 132,
    " Untrained": 90,
    " Novice": 170,
    " Intermediate": 205,
    " Advanced": 280,
    " Elite": 370
}, {
    "Body Weight": 148,
    " Untrained": 100,
    " Novice": 190,
    " Intermediate": 230,
    " Advanced": 315,
    " Elite": 410
}, {
    "Body Weight": 165,
    " Untrained": 110,
    " Novice": 205,
    " Intermediate": 250,
    " Advanced": 340,
    " Elite": 445
}, {
    "Body Weight": 181,
    " Untrained": 120,
    " Novice": 220,
    " Intermediate": 270,
    " Advanced": 370,
    " Elite": 480
}, {
    "Body Weight": 198,
    " Untrained": 125,
    " Novice": 230,
    " Intermediate": 285,
    " Advanced": 390,
    " Elite": 505
}, {
    "Body Weight": 220,
    " Untrained": 130,
    " Novice": 245,
    " Intermediate": 300,
    " Advanced": 410,
    " Elite": 530
}, {
    "Body Weight": 242,
    " Untrained": 135,
    " Novice": 255,
    " Intermediate": 310,
    " Advanced": 425,
    " Elite": 550
}, {
    "Body Weight": 275,
    " Untrained": 140,
    " Novice": 260,
    " Intermediate": 320,
    " Advanced": 435,
    " Elite": 570
}, {
    "Body Weight": 319,
    " Untrained": 145,
    " Novice": 270,
    " Intermediate": 325,
    " Advanced": 445,
    " Elite": 580
}, {
    "Body Weight": 320,
    " Untrained": 150,
    " Novice": 275,
    " Intermediate": 330,
    " Advanced": 455,
    " Elite": 595
}];

alert(getClosest(180)["Body Weight"]);

function getClosest(x) {
    for (var i = data.length - 1; i > -1; i--) {
        if (x > data[i]["Body Weight"]) break
    }
    if (i === data.length - 1) return data[i];
    if (i === -1) return data[0];

    return data[i + +(x > ((data[i]["Body Weight"] + data[i + 1]["Body Weight"]) /...