The perimeter of the rectangle is $8w$ feet.
Work Step by Step
Since the length is $3$ times the width, $w$, we must multiply $w$ by $3$ to find the length. This gives us a length of $3w$. The formula for perimeter of a rectangle is $P=2l+2w$, where $l$ is the length and $w$ is the width. We plug in the values for width and length: $P=2(3w)+2(w)$ We multiply from left to right: $P=6w+2w$ We add to combine like terms: $P=8w$