The perimeter of triangle ABC is 4x+1,if 2 sides are x+2 and x-1,find the 3rd side

what's the problem?

perimeter is the sum of the sides.
Let z be the third side.

x+2 + x-1 + z = 4x+1
z = 4x+1 - (x+2) - (x-1)
z = 4x+1-x-2-x+1
z = 2x