Here's the code which needs to be modified.

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"use strict";

var $ = function (id) {

return document.getElementById(id);

};

var calculateMpg = function (miles, gallons) {

var mpg = (miles / gallons);

mpg = mpg.toFixed(1);

return mpg;

};

var processEntries = function () {

var miles = parseFloat($("miles").value);

var gallons = parseFloat($("gallons").value);

if (isNaN(miles) || isNaN(gallons)) {

alert("Both entries must be numeric");

} else {

$("mpg").value = calculateMpg(miles, gallons);

}

};

window.onload = function () {

$("calculate").onclick = processEntries;

$("miles").focus();

};

Calculate Miles Per Gallon

Miles Driven:

*

Gallons of Gas Used:

*

Miles Per Gallon

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body {

font-family: Times New Roman, Helvetica, sans-serif;

background-color: white;

margin: 0 auto;

width: 600px;

padding: 0 2em 1em;

border: 3px solid blue;

}

h1 {

color: blue;

margin-bottom: .25em;

}

label {

float: left;

width: 11em;

text-align: right;

}

input {

margin-left: 1em;

margin-right: .5em;

margin-bottom: .5em;

width: 11em;

}

span {

color: red;

}

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In this application, you'll make a couple of quick enhancement to the Miles Per Gallon application, like clearing the two entries if the user double-clicks in the Miles Per Gallon text box. Estimated time: 10-15 minutes, Calculate Miles Per Gallon Miles Driven: Gallons of Gas Used Miles Per Gallon Calculate MPG Open the mpg.html file in this folder: exercises short\ch04 mpg\ Run the application to see that it works just like the one in the book. Then, in the JavaScript in the HTML file, note that there's a clearEntries function that isn't use