6) During each cycle, the velocity v (in mm/s) of a piston is v = 6t - 6t², where t is the time (in s). Find the displacement s of the piston after 0.75 s if the initial displacement is zero. 7) A person skis down a slope with an acceleration (in m/s²) given by 600t a = (60 + 0.5t2)² where t is the time (in s). Find the skier's velocity as a function of time if the initial velocity is zero.