A rectangle is divided into four different triangles, of which the area of the green triangle accounts for 15% of the rectangle, and the area of the yellow triangle is 21cm2 Area, main formula and method

A rectangle is divided into four different triangles, of which the area of the green triangle accounts for 15% of the rectangle, and the area of the yellow triangle is 21cm2 Area, main formula and method

If the area of the rectangle is x, then x-0.15x = 21