(7/10)=((7+a)/(10*7)), what is a equal to (Note: "*" stands for "*").
(7/10)=((7+a)/(10*7))，a等于多少(注："*"号代表"*")．
<gadget id="calculator">7 * 7</gadget>
<output>49</output>

<gadget id="calculator">49 - 7</gadget>
<output>42</output>

<result>42</result>