Answer
$a).$ (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
$N=-w=-mg=735N$
