(39-х)-84=78

To solve the equation \( (39 - x) - 84 = 78 \), follow these steps:

1. Simplify the left side of the equation: \[ 39 - x - 84 = 78 \] This can be further simplified to: \[ -x - 45 = 78 \]

2. Next, isolate the term with \( x \) by adding 45 to both sides: \[ -x = 78 + 45 \] \[ -x = 123 \]

3. Multiply both sides by -1 to solve for \( x \): \[ x = -123 \]

Thus, the solution is: \[ x = -123 \]