Add all the sides up to equal 30 in an equation because you are given the perimeter. The perimeter is the length around a two dimensional shape. This means the perimeter is the length of all the side lengths added together.
(x) + (2x + 2) + (13) = 30
Combine like terms.
3x + 15 = 30
Subtract 15 from both sides.
3x = 15
Divide both sides by 3.