#### Answer

a)
a = 20 m/s^2
b)
a = 10/2 = 5 m/s^2
c)
a = 10 m/s^2

#### Work Step by Step

a)
We know that
F = m x a.
If m is constant, F is directly proportional to acceleration.
So
if the force is doubled, the acceleration is doubled.
So
a = 20 m/s^2.
b)
We know that
F = ma.
If F is constant, mass x acceleration will be constant
If mass is doubled, keeping force constant,
acceleration becomes half.
So
a = 10/2 = 5 m/s^2.
c)
We know that
F = ma
a = F/m.
So if both F and m are doubled, acceleration will be the same.
a = 10 m/s^2.