A, B, C, D, and E are five different integers arranged from small to large. Sum each two of them to obtain the following 8 sums (there are 10 sums with the same sum) : 17, 22, 25, 28, 31, 33, 36, 39, find the average of these five integers.
A、B、C、D、E是从小到大排列的五个不同的整数，把其中每两个数求和，分别得出下面8个和数(10个和数中有相同的和数)：17，22，25，28，31，33，36，39，求这五个整数的平均数．
<gadget id="calculator">7 + 10 + 15 + 18 + 21</gadget>
<output>71</output>

<gadget id="calculator">71 / 5</gadget>
<output>71/5 = around 14.2</output>

<result>71/5 = around 14.2</result>