the formula for perimeter is:

P = 2L + 2W

the width, W, is 2ft more then half the length, L.

So W equals 2 more than  times L.

So W = 2 more than L

To make something 2 more than it is, you add 2 to it.

So W = L + 2

Now go back to the formula

P = 2L + 2W.

Since "the perimeter of a rectangle is 40 ft", put 40 where the P is

and (L + 2) where the W is

40 = 2L + 2(L + 2)

Can you solve that for L? If not post again asking how. 

Answer: L = 12

Then you go back to the equation:

W = L + 2

and substitute 12 for L

and you get 8

So the length is 12 feet and the width is 8 feet.

Edwin