Mom bought 5 catties of beef and 5 catties of ghee, and the total cost was 215 yuan. The unit price of each catty of beef was 18 yuan. How much is each catty of butter.
妈妈买了5斤牛肉和5斤酥油，一共用了215元，每斤牛肉的单价是18元，每斤酥油是多少元．
<gadget id="calculator">18 * 5</gadget>
<output>90</output>

<gadget id="calculator">215 - 90</gadget>
<output>125</output>

<gadget id="calculator">125 / 5</gadget>
<output>25</output>

<result>25</result>