Next, consider the $\mathrm{FBD}$ for the small gear.

The small gear must be in equilibrium; therefore, the sum of moments about shaft $\mathrm{B}$ must equal zero.

$\sum _{}{\mathrm{M}}_{\mathrm{B}}={\mathrm{T}}_{\mathrm{small}}-\mathrm{F}\times {\mathrm{R}}_{\mathrm{small}}=0$