Teacher Zhang brought 50 yuan to buy 9 boxes of milk, each box of milk is 4 yuan, how much should I get back?
张老师带了50元钱去买了9盒牛奶，每盒牛奶4元，应该找回多少元？
<gadget id="calculator">4 * 9</gadget>
<output>36</output>

<gadget id="calculator">50 - 36</gadget>
<output>14</output>

<result>14</result>