P = 2(l + w) < perimeter of a rectangle
P = 102 meters
l = 6 + 2w
w = w
102 = 2[(6 + 2w) + w]
102 = 2(6 + 2w + w)
102 = 2(6 + 3w)
102 = 12 + 6w
102 - 12 = 6w
90 = 6w
90/6 = w
15 = w or w = 15
l = 6 + 2w
l = 6 + 2(15)
l = 6 + 30
l = 36
Check.
P = 2(l + w)
102 = 2(36 + 15)
102 = 2(51)
102 = 102
hope this helps and have a great day :)