Answer:
40
Step-by-step explanation:
The formula for the perimeter of a rectangle is P = 2l + 2w. Since the length is 8 times the width, l = 8w. You can plug this into the equation.
P = 2(8w) + 2w
P = 16w + 2w
P = 18w
Now, plug in the given value for perimeter, and solve for w.
90 = 18w
(90)/18 = (18w)/18
5 = w
Since the width is equal to 5, you can now solve for l.
l = 8w
l = 8(5)
l = 40
The length of the diagonal is equal to 40.
