It is known that the ratio of A and B is 4:5, A's number is 18, and B's number is.
已知甲乙两数比是4：5，甲数是18，乙数是多少．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">18 / (4/9)</gadget>
<output>81/2 = around 40.5</output>

<gadget id="calculator">(81/2) - 18</gadget>
<output>45/2 = around 22.5</output>

<result>45/2 = around 22.5</result>