How many newtons of force are represented by the following amount: 3 kg•m/sec²? justify your answer

The definition of 1 Newton is "the force required to accelerate
one kilogram of mass at the rate of one meter per second squared".

That set of units can be written like this:

           1 N  =  1 kg-m/sec² .

So  3 kg-m/sec²  =  3 newtons.