There are 10 copies in a set of "Solving Cases with Sherlock Holmes", and each copy is a yuan. If you buy a set and pay 200 yuan, how much should you get back?
一套《和福尔摩斯一起破案》共有10本，每本a元，买一套付200元，应找回多少元．
<gadget id="calculator">200 - 10</gadget>
<output>190</output>

<result>190</result>