1. The problem is to solve the equation with the number 3 involved, but since the exact equation is not specified, let's consider a simple example: solve for $x$ in $x + 3 = 0$. 2. The formula used here is to isolate $x$ by subtracting 3 from both sides: $$x + 3 = 0 \implies x = 0 - 3$$ 3. Subtracting 3 from both sides, we get: $$x = \cancel{0} - 3$$ 4. Simplifying, we find: $$x = -3$$ 5. Therefore, the solution to the equation $x + 3 = 0$ is $x = -3$. This method applies to any linear equation where you isolate the variable by performing inverse operations.