A$$frac{{{{text{T}}_f}}}{{text{W}}} = left( {frac{{1.21}}{{{{text{C}}_{text{n}}}}}} right) + 0.04$$
B$${{text{T}}_f} = left( {frac{{1.21}}{{{{text{C}}_{text{n}}}}}} right) + 0.04$$
C$${{text{T}}_f} = left( {frac{{1.21}}{{{{text{C}}_{text{n}}}}}} right) + 0.046$$
D$${{text{T}}_f} = 1.24{text{W}} + {text{0}}{text{.046}}$$