The solid$-$circular shaft ABC, having diameter $d=50mm$ and shear modulus $G=100$GPa, is subjected to torques at A and $B$ as shown. What is the required $T_A$ to keep ${}_A=0?$

$2$

$12kN.m$

$16kNm$

$18$ kN$.$m

$20$ kN$.$m

$15kN.m$