Let the length of the rectangular area is x meters. Then
4x+4x3=900,x=270016=168.754x+\frac{4x}{3}=900, \quad x=\frac{2700}{16}=168.754x+34x=900,x=162700=168.75
The length of the rectangular area is 168.75 meters. The width of the rectangular area is 112.5 meters. Base of the triangle is 112.5 meters.