It seems there might be a typo in the problem statement. Could you please clarify the expression or equation involving $x$ that you want to solve? The given information seems to be incomplete or incorrect for solving $x$.

If you meant:

1. Given: $RT = 42$ and
2. Equation: $5x + 2 = 7x + 4$

Then, I can help you solve for $x$.

Please confirm or provide additional details!