Aunt Zhang went to the stationery store to buy 8 pencil boxes, each a yuan, and paid 50 yuan, how much should I get back.
张阿姨到文具商店买8个文具盒，每个a元，付出50元，应找回多少元．
<gadget id="calculator">50 - 8</gadget>
<output>42</output>

<result>42</result>