A small red flag in the shape of a right triangle, the two right-angled sides are 15cm and 20cm respectively, how much m**2 fabric is used to make 15 such small red flags.
一个直角三角形形状的小红旗，两条直角边分别是15cm、20cm，做15面这样的小红旗，用多少m**2的布料．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">15 / 10_000</gadget>
<output>3/2_000 = around 0.0015</output>

<gadget id="calculator">15 * 10 * (3/2_000)</gadget>
<output>9/40 = around 0.225</output>

<result>9/40 = around 0.225</result>