Xiaohong uses 20 yuan to buy pencils. Each pencil is b yuan. If she bought 5 pencils, how much should she get back?
小红用20元钱去买铅笔，铅笔每支b元，买了5支，应找回多少元．
<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<result>15</result>