A trapezoidal vegetable field has an area of 142 square meters, its upper base is 14.5 meters, and its lower base is 21 meters. What is the height of this trapezoidal vegetable field?
一块近似梯形的菜地，面积是142平方米，它的上底是14.5米，下底是21米，这块梯形菜地的高是多少米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">14.5 * (1/2)</gadget>
<output>7.25</output>

<gadget id="calculator">21 * (1/2)</gadget>
<output>21/2 = around 10.5</output>

<gadget id="calculator">7.25 + (21/2)</gadget>
<output>17.75</output>

<gadget id="calculator">142 / 17.75</gadget>
<output>8</output>

<result>8</result>