Let mass be:

Question

m1=0.100 kg
m2=0.300 kg
m3=0.500 kg
(a.)Compute for the acceleration of the system if the table is frictionless.
(b.)Compute the acceleration of the system if the coefficient of the friction between the m2 and the table is 0.400.

You can't compute acceleration without knowing the force, F. Is there a pulley somewhere?

It is unclear what is meant by "the system". You need to provide a description of the system of threee masses. Your question probably came with a Figure.

Try using Newton's law,
F = m a.
"a" is the acceleration.
Someone will be glad to critique your work.