Moments question please help!

As he walks towards end A, the upwards force at Q decreases until it reaches zero (which will be after he's passed B). At this point he's balancing just on point B, so if he carries on going, end E will start moving upwards. This is because his weight will provide an anti-clockwise moment about B, and the weight of the plank provides a clockwise moment. When Q=0 these will be equal and opposite so it balances. As he goes further to the left, the moment of his weight will increase so Q would need to act downwards to cancel it which isn't possible so there's a net anti-clockwise moment about B and the plank will rotate in that direction

oh right - sorry! If you take moments about A, then you get 760*l = 220*1.25 because Q=0 and P is acting through B so l = 220*1.25/760 = 0.362m (3sf)

Why wouldn't it be moment of the plank about B giving:

220N x (220/2 -0.6) = 760*l

Then the value l is equal to the distance from B moving left, so the distance from A is 0.6m minus this?

.........if anybody understands what I mean...........?