There is a kind of fabric in Jinjia Department Store, which sells for 12.5 yuan per meter. Aunt Zhang buys 4 meters of fabric for 100 yuan. How much should she get back?
金甲百货商店有一种布料，每米售价12.5元，张阿姨用100元买4米这样的布料，应找回多少元？
<gadget id="calculator">12.5 * 4</gadget>
<output>50</output>

<gadget id="calculator">100 - 50</gadget>
<output>50</output>

<result>50</result>