Explanation:
The perimeter of a rectangle = 2L + 2W = 98.
W is 15 less than L, or L - 15 = W, or W + 15 = L
Substituting from Eq 2 back into Eq 1,
2(W+15) + 2W = 98
2W + 30 + 2W = 98
4W + 30 = 98
4W = 68
W = 17
Recalling L = W+15
L = 17 + 15 = 32
Now to check our solution
Does the perimeter = 98?
2(32) + 2(17) = ??
64 + 34 = 98
Done!