Answer:
4x -8
Step-by-step explanation:
The perimeter is the sum of the side lengths:
P = a + b + c
7x = (x +3) +(2x +5) +c . . . . fill in the given information
7x = 3x +8 + c . . . . simplify
4x -8 = c . . . . . . . . . subtract (3x+8) from both sides
The missing side is 4x-8.
