\(C = {C_V} + \frac{R}{{1 - n}}\) \(\therefore C - {C_V} = \frac{R}{{1 - n}}\)
\(\therefore 1 - n = \frac{R}{{C - {C_V}}}\) \(\therefore 1 - \frac{R}{{C - {C_V}}} = n\)
\(\therefore n = \frac{{C - {C_V} - R}}{{C - {C_V}}} = \frac{{C - {C_V} - {C_P} + {C_V}}}{{C - {C_V}}}\)
\( = \frac{{C - {C_P}}}{{C - {C_V}}}\left( {{C_P} - {C_{V = R}}} \right)\)