# Write a function rule for the perimeter of a rectangle whose length is 6 feet more than its width. What is the perimeter of the rectangle when its width is 12 feet?

Oct 18, 2017

$P = 4 w + 12$

The perimeter of the rectangle when $w = 12$ is $60$ feet.

#### Explanation:

The perimeter of a rectangle is equal to 2 times the length $l$ plus 2 times the width $w$.

If we know that $l = w + 6$, then we can substitute this into the equation and simplify it.

$P = 2 w + 2 l$

$P = 2 w + 2 \left(w + 6\right)$

$P = 2 w + 2 w + 12$

$P = 4 w + 12$

This is our function for perimeter. Now, if the width is 12, we can simply plug in $12$ to this equation and evaluate it for $P$.

$P = 4 \left(12\right) + 12$

$P = 48 + 12$

$P = 60$

So the perimeter of the rectangle is 60 feet.