The sum of (1/2) of number A and (3/7) of number B is 30, the sum of number A and number B is 60, find the number of A.
甲数的(1/2)与乙数的(3/7)的和是30，甲数与乙数和是60，求甲数．
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">60 * (3/7)</gadget>
<output>180/7 = around 25.714286</output>

<gadget id="calculator">30 - (180/7)</gadget>
<output>30/7 = around 4.285714</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) - (3/7)</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">(30/7) / (1/14)</gadget>
<output>60</output>

<result>60</result>