When a=12, b=8, h=15, how much is (1/2)(a+b)h=.
当a=12、b=8、h=15时，(1/2)(a+b)h=多少．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">12 + 8</gadget>
<output>20</output>

<gadget id="calculator">(1/2) * 20 * 15</gadget>
<output>150</output>

<result>150</result>