The position of a particle moving on the x- axis is x= 7.8 + 9.2t -2.1t³ where x is in meters and t is in seconds. What's it's velocity at t= 3.5 seconds and is the velocity constant or continuously changing?​

Amass weighing 24 pounds, attached to the end of a spring, stretches it 4 inches. initially, the mass is released from rest from a point 8 inches below the equilibrium position. find the equation of motion. (use g = 32 ft/s2 for the acceleration due to gravity.)