Answer:
width = 6 ft
length = 21 ft
Step-by-step explanation:
Forming algebraic expressions and finding the dimensions of a rectangle:
 Width = w ft
 length =  3*w + 3 = (3w + 3) ft
       2l +2w = P
 2(3w + 3) + 2w = 54
Use distributive property to open the brackets,
 2*3w + 2*3 + 2w = 54
    6w + 6 + 2w = 54
Combine like terms,
     6w + 2w + 6 = 54
        8w  + 6  = 54
Subtract 6 from both sides,
           8w   = 54 - 6
             8w = 48
Divide both sides by 8
              w = 48 ÷ 8
              [tex]\sf \boxed{\bf w = 6 \ ft}[/tex]
l = 3w + 3
 = 3*6 + 3
 = 18 + 3
l = 21 ft
