You have the lenght that is 3w, so lenght is the third part and the width the first part.
You assign the value 3 to l and the value 1 to w
Of course, you have to do the "semiperimeter" or you'll get double sides.
Semiperimeter = 26/2 = 13 ft.
You sum the parts
3+1 = 4
13/4 = 3,25 ft. (1 part)
3,25*1 = 3,25 ft. (Widht)
3,25*3 = 9,75 ft. (Lenght)
You can solve it even as an equation
You put x the lenght, the width is 3x
x+3x = 13
4x = 13
x = 3,25
w = 3*3,25 = 9,75
