It is known that a△b=(a+b)/2, a▽b=a*ba, then 10△(5▽7)=how much.
已知a△b=(a+b)/2，a▽b=a*b-a，则10△(5▽7)=多少．
<gadget id="calculator">5 * 7</gadget>
<output>35</output>

<gadget id="calculator">35 - 5</gadget>
<output>30</output>

<gadget id="calculator">10 + 30</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>