Since the ratio of width to length is 2:3, that is a total of 5 parts.
Multiply this by 2 (P = 2L + 2W) = 10 parts.
120/10 = 12
Each part = 12
W:L
12*2:12*3 = 24:36
CHECK
2(24) + 2(36) ??=?? 120
48 + 72 ??=?? 120
120 = 120 checks
Length = 36 ft
Width = 24 ft