There are two types of matrices. One is REF and the other is what makes REF simpler--RREF. We use RREF to solve for REF because it makes the solution easy to find. RREF is displayed in your problem... it means that it's already solved, so the answers are already given on the right side, which is -3,2,-1. This only works with the combination provided (with the 0s and 1s). Otherwise, you'd have to solve.
