Let us assume width of the rectangle = w cm.
Length of the rectangle is three times the width.
We took width by w.
Therefore, three times of w = 3*w = 3w.
That is the length of the rectangle.
Perimeter of the rectangle is given by following formula.
Perimeter = 2*length + 2 * width.
We also given that perimeter is at most 112.
Note: "At most" pharse represents less than or equal to.
Therefore, we could setup an inequality as
2*length + 2 * width ≤ 112
Plugging length = 3w and width =w, we get
2*3w + 2*w ≤ 12
or 2w +2*3w ≤ 12.
Therefore, 2w +2*3w ≤ 12 inequality models the realationship between the width and the perimeter of the rectangle.