The length of a rectangle is 10 centimeters. If the length is increased by 3 centimeters, the area will increase by 15 square centimeters. What is the area of the original rectangle?
一个长方形长是10厘米，长增加了3厘米之后，面积增加了15平方厘米．那原来的长方形的面积是多少．
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">10 * 5</gadget>
<output>50</output>

<result>50</result>