The length of a rectangle is 9 meters, which is its width if the perimeter of this rectangle is 26 meters.

The perimeter of a rectangle is the sum of the length and width of the rectangle multiplied by 2. Let’s write the formula for the perimeter of a rectangle:
P = (a + b) × 2,
where a is the length of the rectangle, b is the width.
Let us express the width, b, from the formula for the perimeter:
P = 2a + 2b,
2b = P-2a,
b = (P-2a): 2.
Find the width b by substituting the length and perimeter in the formula:
b = (26-2 × 9): 2 = (26-18): 2 = 8: 2 = 4 m.
Answer: The width of the rectangle is 4 m.