A is 72, which is 80% of B, how much is B.
甲是72，是乙的80%，乙是多少．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">72 / (4/5)</gadget>
<output>90</output>

<result>90</result>