The ratio of the numbers A and B is 4:3, the number B is 30, what is the number A?
甲乙两数的比是4：3，乙数是30，甲数是多少．
<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>