A parallelogram and a triangle have the same base and height. It is known that the sum of their areas is 30 square centimeters, what is the area of the triangle in square centimeters.
一个平行四边形和一个三角形等底等高．已知它们面积之和是30平方厘米，三角形的面积是多少平方厘米．
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">30 * (1/3)</gadget>
<output>10</output>

<result>10</result>