​ what is the perimeter of PQR

The two triangles are congruent, so:

PR = SU

3y - 2 =y + 4    Subtract y from both sides 

3y - 2 - y = 4    Add 2 to both sides

3y - y =4 + 2

2y = 6                Divide both sides by 2

y =6/2

y = 3 

Sub 3 for y in 3y - 2

3*3 - 2 =7 Ft - Length of side PR

Perimeter of PQR =4 + 6 + 7 =17 Feet