The students do handwork, the ratio of the number of boys and girls is 2:3, the whole class averages 18 pieces per person, girls make 20 pieces per person on average, and how many pieces per boy do on average.
同学们做手工，男女生人数之比为2：3，全班平均每人做18件，女生平均每人做20件，男生平均每人做多少件．
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">18 * 5</gadget>
<output>90</output>

<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">90 - 60</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>