You solve this through error and trial.
The is to get two matching numbers at both sides.
X 2x + 3 = 3 (x + 1) - x Answer
0 2(0) + 3 = 3 (0 + 1) - 0 3 = 3
1 2(1) + 3 = 3 (1 + 1) - 1 5 = 5
You do this all the way to ten. So far, we know x = 0 and x = 1 is correct