Answer:
Perimeter = 2(Length + Width) | Formula for perimeter
102 = 2(3m + m) | Plug in value of length and width
102 = 2(4m) | Combine like terms
102 = 8m | Distribute 2
8m = 102 | Flip LHS and RHS
m = 12.75m | Divide by 8 on both sides
Answer m = 12.75 ft