The next step is the backward substitution step. The last row is multiplied by $c_{N-3}/b_{N-2}$ and subtracted from the second to last row, thus eliminating $c_{N-3}$ from the last row. The general backward substitution procedure is $$c_i = 0,$$ and $$f_{i-1} = f_{i-1} - \frac{c_{i-1}}{b_i}f_i$$ All that remains to be computed is the solution, which is the very straight forward process of $$x_i = \frac{f_i}{b_i}$$