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