The lengths of the upper base, lower base and height of a right-angled trapezoid are a, b and h respectively (unit: meter). If ah=17, bh=25, what is the area of this right-angled trapezoid in square meters?
一个直角梯形的上底、下底和高的长度分别是a、b和h(单位：米)．如果ah=17，bh=25，那么这个直角梯形的面积是多少平方米．
<gadget id="calculator">17 + 25</gadget>
<output>42</output>

<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<result>21</result>