${\mathrm{T}}_{\mathrm{C}}=\frac{0.01745 \mathrm{rad}+(20,000 \mathrm{N}-\mathrm{mm}){\displaystyle \frac{{\mathrm{L}}_1}{{\mathrm{J}}_1{\mathrm{G}}_1}}}{{\displaystyle \frac{{\mathrm{L}}_1}{{\mathrm{J}}_1{\mathrm{G}}_1}}+{\displaystyle \frac{{\mathrm{L}}_2}{{\mathrm{J}}_2{\mathrm{G}}_2}}}$

Substitute the shaft properties into the above equation to compute the value for external torque ${\mathrm{T}}_{\mathrm{C}}$.