The perimeter of a rectangle is equal to P = 2l+2w where l=length and w=width. Here the length is 5 feet longer than the width or 5+w. This means the width is w. Substitute P = 34, l=5+w and w into the perimeter equation. Then solve for w.
34 ≤ 2*(5+w) + 2w
34 ≤ 10+2w+2w
34 ≤ 10+4w
24 ≤ 4w
6 ≤ w
This means the width must be at least 6 so the solution is w ≥ 6.