The price ratio of a coat to a pair of trousers is 5:4, and the price of a coat and a pair of trousers is 180 yuan. How much should it cost to buy a pair of trousers?
一件上衣与一条裤子的价钱的比是5：4，一件上衣和一条裤子的价钱是180元，如果买一条裤子应花多少元．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

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

<gadget id="calculator">180 * (4/9)</gadget>
<output>80</output>

<result>80</result>