The first step is simply to combine like terms. $$\begin{aligned} -3 + 6 &= -4B - B - 27 \\ 3 &= -5B - 27 \\ 3 \mathbf{{} + 27}&= -5B - 27\mathbf{{} + 27} \\ 30 &= -5B \\ \frac{30}{-5}&= \frac{-5B}{-5} \\ -6 &= B\\ B &= -6 \end{aligned}$$ The solution to this equation is $-6$. To stress that this is a value assigned to $B$, some report $B = -6$. We can also say that the solution set is $\{-6\}$, or that $B\in\left\{-6\right\}$. If we substitute $-6$ in for $B$ in the original equation $-3+6=-4B-B-27$, the equation will be true. Please check this on your own; it is an important habit.