2 times a plus the product of 3 times 5, the sum is 20, use the equation to solve a.
a的2倍加上3乘5的积，和是20，用方程求解a．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>