Rectangle poster is 3 times as long as wide and perimeter is 24 inches

The length is 9 inches and the width is 3 inches.

Step-by-step explanation:

Rectangular poster is 3 times as long as it is wide.

Its perimeter is 24 inches.

Let its width be x inches;

Its length will be equal to 3x inches.

Perimeter is given by 2 (length + width)

2 (3x + x) = 24 inches

8x = 24 inches, x = 3 inches

So the width of the poster is 3 inches and the length is 9 inches.