A trapezoidal wheat field has an upper base of 400 meters, a lower base of 500 meters, and a height of 400 meters. If about 4.5 tons of wheat can be harvested per hectare, how many tons of wheat can be harvested in this wheat field?
一块梯形麦田，上底是400米，下底是500米，高是400米．如果每公顷能收小麦约4.5吨，这块麦田大约能收小麦多少吨？
<gadget id="calculator">400 + 500</gadget>
<output>900</output>

<gadget id="calculator">400 / 2 / 10_000</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">900 * (1/50) * 4.5</gadget>
<output>81</output>

<result>81</result>