The length is 17 feet and the width is 14 feet.
Let l be length and w be width.
w = l - 3 and A = lw
Thus
238 = l * (l-3)
When you solve for L, you get 17 and -14. Because you can't have a negative number as a distance, the answer has to be 17.
Plug in 17 into w = l - 3 and you get w = 14