The ratio of A and B is 3:4. The number of B is 12, what is the number of A?
甲、乙两数的比是3：4．乙数是12，甲数是多少．
<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<result>9</result>