Answer
The force required from the extensor muscle is about 970N
Work Step by Step
We sum the torques about the elbow joint to solve for the force required from the extensor muscle,$F_M$. Therefore;
$(+ \circlearrowleft) \sum \tau=0$
$F_M*0.025m-2.3kg*g*.12m-7.3kg*g*.30m=0$
$F_M=(2.3kg*g*.12m+7.3kg*g*.30m)/(0.025m)$
$F_M=(2.3kg*9.8m/s^2*.12m+7.3kg*9.8m/s^2*.30m)/(0.025m)$
$F_M\approx970N$
The force required from the extensor muscle is about 970N.