$a).$ (3) two $b).$ 1470N, 735N.
Work Step by Step
a). There are two forces acting on the crate: the weight and the normal force. The normal force is such that its difference with weight gives the crate upward acceleration. b). N+w=ma N=$ma-w=ma-mg=m(a-g)=75(9.8+9.8)=1470N$ [we take upwards as positive] On the ground, the normal force would be equal in magnitude to the weight $N=-w=-mg=735N$