Verified answer

work out the angle of the ladder then calculate the vertical and horizontal component forces

let the length of the ladder = L and the man's weight = W.

Angle A of ladder with ground = cos^-1(3/5) = 53.13°.

The moments about the standpoint amount to 0 because the ladder is in equilibrium.

moment by man: W*cosA*(L/2)

moment by wall on ladder: N*sinA*L where N is the normal force by the wall on the ladder.

W*cosA*(L/2) = N*sinA*L

1/2*W*cosA = N*sinA

N = WcosA/(2sinA)

N = 800*cos53.13/(2*sin53.13)

N = 300 N

OG