There were 40 questions in a math competition. Ding Le got it right (4/5), and Zhang Qing got Ding Le's right number (7/8). How many questions did Zhang Qing get wrong?
一次数学竞赛中共有40道题，丁乐做对了(4/5)，张青做对的道数是丁乐的(7/8)，张青做错了几道题？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">40 * (4/5) * (7/8)</gadget>
<output>28</output>

<gadget id="calculator">40 - 28</gadget>
<output>12</output>

<result>12</result>