Net force on a 12 kg box accelerating at 2.5 m/s^2

Assumptions: the listed acceleration is the net acceleration of the box.
Use Newton's second law: 
F_net = ma
F_net = (12 kg)(2.5 m/s^2)
F_net = 30 kg*m/s^2
Since 1 N = 1 kg*m/s^2, F_net = 30 N.