The base length of a triangle is 10m. If the base is extended by 4m, the area will increase by 7m**2. Please find out the area of the original triangle in square meters?
一个三角形的底长是10m，如果底边延长4m，那么面积就增加7m**2，请你求出原来三角形的面积是多少平方米？
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">(7/2) / 2</gadget>
<output>7/4 = around 1.75</output>

<gadget id="calculator">10 * (7/4)</gadget>
<output>35/2 = around 17.5</output>

<result>35/2 = around 17.5</result>