The force F on an object is the product of the mass m and the acceleration a. In this problem, assume that the mass and acceleration both depend on time t, hence so does the force. That is, F(t) = m(t) * a(t). At time t = 7 seconds, the mass of an object is 2 grams and changing at a rate of -1 g/s. At this same time, the acceleration is 8 m/s^2 and changing at a rate of -4 m/s^3. By the product rule, the force on the object is changing at the rate of _____________ (unit).