To solve the equation, we can follow these steps:

1. Simplify the expression on the left side of the equation:
4.2^3 = 4.2 * 4.2 * 4.2 = 74.088

2. Substitute the simplified expression back into the equation:
3x - 74.088 = 19 + (-15)

3. Simplify the right side of the equation:
19 + (-15) = 4

4. Rewrite the equation:
3x - 74.088 = 4

5. Add 74.088 to both sides of the equation to isolate the variable:
3x - 74.088 + 74.088 = 4 + 74.088
3x = 78.088

6. Divide both sides of the equation by 3 to solve for x:
3x/3 = 78.088/3
x = 26.029