A rectangle has sides x and y.
x=6-4y
y= 15over2 -5x
The area is 15over2 x - 5over4 xsquared.
I don't know where the second part of the area comes from.
I'll have to write the whole question. A window is y high and x long. There are 12 square sections layed out 3 by 4 so y is 1.33 times x. 30 metres of strip is used around all the pieces.
I have to show that the area is given by the formula 15/2x-5/4x^2.