The ratio of number A to number B is 4:9, the number A is 72, and the number B is x. Find the value of x by solving the ratio.
甲数和乙数的比是4：9，甲数是72，乙数是x，用解比例的方法求x的值．
<gadget id="calculator">72 * 9</gadget>
<output>648</output>

<gadget id="calculator">648 / 4</gadget>
<output>162</output>

<result>162</result>