The ratio of the numbers A and B is 4:5, and their average is 90, what is the number B?
甲、乙两数的比是4：5，且它们的平均数是90，那么乙数是多少．
<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">180 * (5/9)</gadget>
<output>100</output>

<result>100</result>