The length of Sally’s garden is 4 meters greater than 3 times the width. The perimeter of her garden

The length of Sally’s garden is 4 meters greater than 3 times the width. The perimeter of her garden is 72 meters

A garden is a rectangle, which has perimeter P of:
P = 2l + 2w

With P = 72, we have:
2l + 2w = 72

We're also given:
l = 3w + 4

We substitute this into the perimeter equation for l:
2(3w + 4) + 2w = 72
6w + 8 + 2w = 72

To solve this equation for w, we type it in our search engine and we get:
w = 8

Now, to solve for l, we substitute w = 8 into our length equation above:
l = 3(8) + 4
l = 24 + 4
l = 28