First, let's define our variables.
Let's call our width X(given)
and our length, since it's 10 shorter than 3 times the width, we can call our length:
3x-10
So, the perimeter of a rectange is equal to 2 times the length + 2 times the width.
So, when we plug our values in, we get
[tex]2(3x-10)+2x\\6x-20+2x\\8x-20[/tex]
The perimeter is 8x-20
