The base of a triangle is 9 cm long and the height is 4 cm shorter than the base. What is the area of the triangle?
一个三角形的底长9厘米，高比底短4厘米，这个三角形的面积是多少．
<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">9 * (5/2)</gadget>
<output>45/2 = around 22.5</output>

<result>45/2 = around 22.5</result>