Students in class 61 of a certain school do handicrafts. The ratio of male to female students is 2:3. The average class makes 18 pieces, male students make 15 pieces on average, and how many female students do on average?
某校六1班同学做手工，男女生人数之比为2：3，全班平均每人做18件，男同学平均每人做15件，女同学平均每人做多少件？
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

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

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

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

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

<result>20</result>