The two art groups drew a total of 450 pictures. There were 13 people in the first group, and 4 people in the second group than the first group. How many pictures did each of the two groups draw on average?
两个美术组一共画了450张图画．第一组13人，第二组比第一组4人．两组平均每人画了多少张图画？
<gadget id="calculator">13 + 13 + 4</gadget>
<output>30</output>

<gadget id="calculator">450 / 30</gadget>
<output>15</output>

<result>15</result>