The answer is no solution.
Step-by-step explanation:
Because of pemdas, first, solve the parentheses. It becomes 4.2x + 3, as multiplying by 0.5 caused the same effect as if you were to divide by 2. Now if you look at the problem, it is just 4.2x - 3 = 4.2x + 3. Even though the symbols are different, they are still equal to eachother.