(39-х)-84=78

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

1. Start with the equation: \[ (39 - x) - 84 = 78 \]

2. Simplify the left side: \[ 39 - x - 84 = 78 \] \[ -x - 45 = 78 \]

3. Now, isolate \( -x \) by adding 45 to both sides: \[ -x = 78 + 45 \] \[ -x = 123 \]

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

So the solution is: \[ x = -123 \]