Expand the radius of a sector to 3 times, and reduce its central angle to half of the original. The area of the obtained sector is 70 square centimeters larger than the original area. What is the area of the original sector?
将一个扇形的半径扩大为3倍，同时将他的圆心角缩小为原来的一半，得到的心扇形面积比原来的面积增加70平方厘米求，原来扇形的面积？
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">(9/2) - 1</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">70 / (7/2)</gadget>
<output>20</output>

<result>20</result>