To find the area of a rectangle, it is l×w=A
We can use bits of information to fill in the variables.
The playground covers 4500 m². A=4500
l×w=4500
The length is 40 m longer than the width.
L=W+40
w(w+40)=4500
Let's multiply.
W²+40w=4500
I solved this by making a graph and finding when the two sides intersect (as shown in the picture below).
So since the width is 50, that means the length is 90.