Answer
500 N.
Work Step by Step
The scaffold is in equilibrium, and the sum of the forces on it is zero.
The upward forces are 800 N and the unknown x.
The downward forces are 500 N from the first painter, 400 N due to the weight of the scaffold, and 400 N from the second painter.
$$800 N + x - 500 N - 400 N - 400 N = 0$$
$$x = 500 N$$
