The bottom of a trapezoidal paddy field is 45 meters. If the upper base is increased by 15 meters, the trapezoidal paddy field becomes a square. Find the area of the trapezoidal paddy field.
一块梯形稻田下底为45米，如果上底增加15米，这块梯形稻田就变成一个正方形，求这块梯形稻田的面积．
<gadget id="calculator">45 - 15</gadget>
<output>30</output>

<gadget id="calculator">45 + 30</gadget>
<output>75</output>

<gadget id="calculator">45 / 2</gadget>
<output>45/2 = around 22.5</output>

<gadget id="calculator">75 * (45/2)</gadget>
<output>3_375/2 = around 1_687.5</output>

<result>3_375/2 = around 1_687.5</result>