This answer is vague in whether they want you to add just the length and the width or if they are asking that the perimeter is 96 yards. I will show both.
The length is width - 12. Lets call width x.
Length = x - 12
Width = x
So if it is just the sum of the length and width, it would be x + x -12 = 96
2 x - 12 = 96
2 x = 108
x = 54
Length would be 54 - 12 = 42 yards.
If it was perimeter, the values would be the same except 2(x) + 2(x-12) = 96
2x + 2x -24 = 96
4x = 120
x = 30
Length = 30 - 12 = 18 yards
I hope this helps :-)
