Question 311208
A = L*W

84 = LW

At this point, you can solve for either L or W. 

I will solve for W.

84 - L = W

The perimeter of a rectangle is found using P = 2L + 2W.

P = 2L + 2(84 - L)

P = 2L + 168 - 2L

P = 168 inches