Answer:
7x+7
Explanation:
The perimeter of a triangle can be found by adding all the side lengths up.
The 3 side lengths are 3x, 3x+7 and x.
We can add these lengths together to find the perimeter.
3x+3x+7+x
Combine like terms. Add all the terms with a variable (x): 3x, 3x and x.
(3x+3x+x)+7
7x+7
The perimeter of the triangle is 7x+7