B). We've known since Galileo ... for roughly the past 375 years ...
that when there is no air resistance, all objects fall with the same
acceleration.
The big rock, the small rock, a feather, a backpack, a school bus,
a piece of tissue, and a battleship, all fall with the same acceleration,
and reach the same speed. If you drop them at the same time, then
they hit the ground at the same time.
On Earth, the acceleration due to gravity is about 9.8 m/s², but this
problem tells you to use 10 . OK.
C). Then the gravitational field strength on Earth is 10 Newtons per kg.
Just like it says at the top, above the picture.