To solve the equation 84 + (2x - 3) = 129, we can start by simplifying the expression inside the parentheses:

2x - 3 = 129 - 84

Next, we can simplify the right side of the equation:

2x - 3 = 45

To isolate the variable x, we can add 3 to both sides of the equation:

2x - 3 + 3 = 45 + 3

This simplifies to:

2x = 48

Finally, we can solve for x by dividing both sides of the equation by 2:

2x/2 = 48/2

This simplifies to:

x = 24

Therefore, the solution to the equation is x = 24.