A particle of 1.6 kg moves all along an x axis, being propelled through a variable force directed all along that axis. Its position is given by x = 3.0 m + (4.0 m/s)t + ct2 - (1.2 m/s3)t3, with x in meters and t in seconds. The factor c is a constant. At t = 3.0 s, the force on the particle consists of a magnitude of 36 N and is in the negative direction of the axis. Determine c?