l - lenght
w - width
l - w = 5 → l = 5 + w
26 m - perimeter
l + l + w + w = 2l + 2w - perimeter
substitute l = 5 + w:
2(5 + w) + 2w = (2)(5) + (2)(w) + 2w = 10 + 2w + 2w = 10 + 4w
The equation:
10 + 4w = 26 subtract 10 from both sides
4w = 16 divide both sides by 4
w = 6
Answer: The width = 6 m.