The ratio of the numbers A and B is 3:7, the number B minus the number A is 20, what is the number B?
甲乙两数的比是3：7，乙数减甲数得20，乙数是多少．
<gadget id="calculator">7 - 3</gadget>
<output>4</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 7</gadget>
<output>35</output>

<result>35</result>