The number of A is 30, which is (2/5) of the number of B. What is the number of B?
甲数是30，是乙数的(2/5)，乙数是多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / (2/5)</gadget>
<output>75</output>

<result>75</result>