In order to find this we first need to set up variables for the length and the width. Since we don't know anything about the width, we'll set it as x. Then, we know the length is equal to ten more than three times the width. Since the width is x, we can write the length as 3x + 10. Now we can use the formula for the perimeter of a rectangle to solve for x.
2l + 2w = P
2(3x + 10) + 2(x) = 60
6x + 20 + 2x = 60
8x + 20 = 60
8x = 40
x = 5
Now that we have a value for x, we can plug into the length equation and find the length.
