i guess you meant triangle.
Also, this is a U-shaped quadratic in x, hence we can solve for minimum area, not maximum, using the derivative.
Differentiating this wrt x and equate the result to zero, gives x corresponding to minimum area.
You will see that it's U-shaped when you multiply out the factor on the RHS of the area equation.
Hence, the maximum area corresponds to x=0 or x=60
Sum of the areas =
For maximum area, compare the area when x=0 to the area when x=60.