The perimeter, P, of a rectangle is the sum of twice the length and twice the width.

P = 2 (l+w) units

P = 2 (5) + 2 (9) units

P = 4x units

P = (l+l) + (w+w) units

P = 2 (x+3) units

The answer is P = 2 (l+w) units.

This is because when you let the perimeter of the rectangle be P, the length of the rectangle be l and the width of the rectangle be w.

The information above can be expressed as the following equation,

P = 2l + 2w

You can then factorise out the common factor, 2.

P = 2 (l+w)

Thus, the answer is P = 2 (l+w) units.