Step 1 :First, we isolate the term with the variable $x$ by subtracting $4$ from both sides of the equation. This gives us $-3^{x-7}=15-4$.
Step 2 :Simplify the right side of the equation to get $-3^{x-7}=11$.
Step 3 :Next, we get rid of the negative sign on the left side by multiplying both sides of the equation by $-1$. This gives us $3^{x-7}=-11$.
Step 4 :Since we cannot have a negative number equal to a power of $3$, there are no solutions to this equation.