The ratio of the numbers A and B is 4:7, the number B is 18 more than the number A, what is the number A?
甲乙两数的比是4：7，乙数比甲数多18，甲数是多少．
<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">18 / 3</gadget>
<output>6</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<result>24</result>