.
1.    Two equations setup and solution
2L + 2W = 282  (the perimeter),   which is simplified to  
L + W = 141,     (1)
L - W =  45.     (2)
--------------------------Add the equations to eliminate W. You will get
2L    = 141 + 45 = 186  ====>  L =  = 93.
Then from (1)  W = 141 - L = 141 - 93 = 48.
Answer.  The dimensions are  93 ft  and  48 ft.
 = 93.
Then from (1)  W = 141 - L = 141 - 93 = 48.
Answer.  The dimensions are  93 ft  and  48 ft.
1.    One equation setup and solution
L      + W +  L     + W = 282    (perimeter)
(W+45) + W + (W+45) + W = 282
4W + 90 = 282  ====>  4W = 282 -90 = 192  ====>  W =  = 48.
The same answer.
 = 48.
The same answer.