A $20\ \text{kg}$ uniform plank $4.0\ \text{m}$ long rests on supports at its ends, A and B. A $50\ \text{kg}$ child stands $1.0\ \text{m}$ from A, as shown. Taking $g = 9.8\ \text{m/s}^2$, how hard does support A push up?

Fig. 1: A uniform plank 4.0 metres long, of mass 20 kilograms, rests on two supports, A at its left end and B at its right end. A child of 50 kilograms stands on it 1.0 metre from A.