Answer
The magnitude of the force at point B from the lower leg bones is $~~3600~N$
Work Step by Step
In parts (a) and (b), we found that there is an upward force of $2700~N$ exerted at point A from the muscle.
Also note that the floor pushes up at point P with a force of $900~N$
Let "up" be the positive direction.
To find the force at point B from the lower leg bones, we can consider the vertical forces exerted on the foot.
We can find $F_B$, the force at point B from the lower leg bones:
$F_{net,y} = 0$
$2700~N+900~N+F_B = 0$
$F_B = -900~N-2700~N$
$F_B = -3600~N$
The magnitude of the force at point B from the lower leg bones is $~~3600~N$.
