There are 36 black keys on a piano, and 20 less white keys than twice as many black keys. How many white keys are there?
钢琴的黑键有36个，白键比黑键的2倍少20个，白键有多少个？
<gadget id="calculator">36 * 2</gadget>
<output>72</output>

<gadget id="calculator">72 - 20</gadget>
<output>52</output>

<result>52</result>