Write the equilibrium equation for the sum of moments about shaft $\mathrm{B}$ to determine the torque applied to the large gear:

$\sum _{}{\mathrm{M}}_{\mathrm{B}}=\mathrm{F}\times {\mathrm{D}}_{\mathrm{large}}/2-{\mathrm{T}}_{\mathrm{large}}=0$