An expanding rectangle has a fixed width of 7 inches and an initial length of 0 inches. The length of the rectangle begins increasing at 2.7 inches per second. Write a formula that expresses the perimeter of the rectangle, P (in inches), in terms of the length of the rectangle, l (in inches).

P = (5.4 inches/sec) t + 14 inches for t > 0

Step-by-step explanation:

A formula for the length of this rectangle is L = (2.7 inches/sec) t, where t is the number of seconds.

The standard formula for the perimeter of a rectangle is P = 2L + 2W.

Substituting (2.7 inches/sec) t for L, we get:

P = 2 ((2.7 inches/sec) t) + 2 (7 inches) for t > 0.

This may be simplified slightly:

P = (5.4 inches/sec) t + 14 inches for t > 0