Answer
$T = 457~N$
Work Step by Step
To find the tension $T$, we can consider the net torque about a rotation axis at the point where the left cable is attached to scaffold 1.
Scaffold 1, scaffold 2, and the box of nails contribute to the clockwise torque about the rotation axis. There is an opposing counterclockwise torque from tension $T$.
We can find $T$:
$(3.00~m)~T-(1.50~m)(50.0~kg)(9.8~m/s^2)-(1.50~m)(30.0~kg)(9.8~m/s^2)-(1.00~m)(20.0~kg)(9.8~m/s^2) = 0$
$(3.00~m)~T = (1.50~m)(50.0~kg)(9.8~m/s^2)+(1.50~m)(30.0~kg)(9.8~m/s^2)+(1.00~m)(20.0~kg)(9.8~m/s^2)$
$T = \frac{(1.50~m)(50.0~kg)(9.8~m/s^2)+(1.50~m)(30.0~kg)(9.8~m/s^2)+(1.00~m)(20.0~kg)(9.8~m/s^2)}{3.00~m}$
$T = 457~N$
