Answer:324 ft^2
Explanation:
We can draw a diagram with x being the width and the length is 4x
___4x____
x | | x
___4x____
since we know the perimeter is 90,
4x+x+4x+x=90
10x=90
x=9
so now we found the width, we can find the height
x=9, 4x=36.
To find the area, multiply by length by the width
9*36=324 ft^2