Triangle area = length * height ÷2

Let the area of a rectangle be x square centimeters.

Among the four triangles in a rectangle, the bottoms of the upper and lower triangles are equal, and they are all rectangular whips. The sum of the heights is exactly equal to the width of the rectangle. Then, add up the areas of these two triangles, that is, length * height (upper) ÷2+ length * height (lower) ÷2= length * height (upper)+height (lower)] = length * height ÷2=x/2.

That is 50+x/7=x/2.

x/2-x/7=50

5x/ 14=50

x=50* 14/5

= 140 (square centimeter)