Problem- Newton's Second Law in 1D

Newton's Second Law of Motion says that the vector sum of the forces acting on an object equals the object's mass times its acceleration.  Mathematically, this is written

∑F = ma

Or, in component form,

∑F_x = ma_x

∑F_y = ma_y

∑F_z = ma_z

1D Problems:

a)  You push a 50-kg sled in the snow with a force of 100 N along the x-direction.  What is the sled's acceleration?

b)  A 5-kg rock falls downward with an acceleration of -9.80 m/s² because of gravity.  Calculate the value of the gravitational force.

c)  Two lions are fighting over a 70-kg gazelle.  The lion on the right pulls to the right with force 400 N and the lion on the left pulls to the left with force 430 N.  What is the acceleration of the gazelle?