Solved: JavaScript/jQuery: Manipulate number in chart tooltip

In this example, if you hover over a point on the chart, the value of x is displayed in a tooltip. I want the value of x*2 to be displayed in the tooltip.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Flot Example</title>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script>
<script type="text/javascript" src="http:////cdnjs.cloudflare.com/ajax/libs/flot/0.8.1/jquery.flot.min.js"></script>
<script type="text/javascript" src="https://raw.github.com/krzysu/flot.tooltip/master/js/jquery.flot.tooltip.min.js"></script>
</head>
<body>
<div id="placeholder" style="width:600px;height:300px;"></div>
<script type="text/javascript">
var format = {
    grid: {
        show: true,
        aboveData: true,
        hoverable: true,
        autoHighlight: true,
        mouseActiveRadius: 20
    },
    series: {
        lines: {
            show: true,
        },
        points: {
            show: true
        }
    },
    xaxis: {
        show: true
    },
    yaxis: {
        show: true
    },
    tooltip: true,
    tooltipOpts: {
        content: "%x * 2 = ???",
        shifts: {
            x: -30,
            y: -50
        }
    }
};
$(document)
    .ready(function () {
        var d1 = [];
        for(var i = 0; i < 61; i++)
            d1.push([i, Math.sin(i)]);
        $.plot($('#placeholder'), [{
            label: "Example",
            data: d1,
    }], format);
});
</script>
</body>
</html>

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