Some help would be very much appreciated !!

a = 6 m/s².

Explanation:

If we have the object with mass of 75 kg and force on it is 50 N then according to given statement its acceleration is 3m/s².

When we double the force on same object by keeping the mass constant then the acceleration will also double. It means force will be 100 N and acceleration will be 6 m/s².

But if we we increase the mass then acceleration goes to decrease.

So,

mass = 75 kg

F = 50 N

a = 3m/s²  then by double the amount of force,

mass = 75 g

F = 100 n

a = 6 m/s².

This is actually explain the newton second law. This law stated that the acceleration of object is depend upon its mass and force acting on it.

F=  m. a

a = F/m

Thus acceleration is directly proportional to the force and inversely  proportional to the mass.