The lengths of the two sides of a right triangle are two prime numbers whose sum is 18 cm. What is the area of this right triangle in square centimeters?
一个直角三角形两条直角边的长是两个质数，它们的和是18厘米．这个直角三角形的面积是多少平方厘米？
<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">11 * (7/2)</gadget>
<output>77/2 = around 38.5</output>

<result>77/2 = around 38.5</result>