Question

A force of 45 N is exerted on an object, resulting in an acceleration of 5 m/s2 for the object. What will the object's acceleration be if the force doubles?

Answer 1

F=ma
the mass is constant, if we dont consider friction, then if F doubles a doubles with it

Answer 2

The object's acceleration is directly proportional to the net force
acting on it.

If that force of 45N is the ONLY force acting on the object, then the
object's acceleration will double (to 10 m/s²) when that force doubles.

If there are other forces acting on the object besides the 45N, or
if there is friction or air resistance, then we can't tell until we know
all about the other forces.