To solve the equation \( x - 78 = -5 \), you can add a number to both sides to isolate \( x \).
First, let's determine what number should be added. We want to get rid of the \(-78\) on the left side, so we can add \(78\) to both sides:
\[ x - 78 + 78 = -5 + 78 \]
This simplifies to:
\[ x = 73 \]
Thus, the number that should be added to both sides of the equation is \(78\).