The graph oi: the velocity (in km/h) of a car that is accelerating is shown in the figure, where t is measured in seconds. v lkmlhl 80 60 4O 20 1' (seconds) 4 8 12 (a) Use the midpoint rule with n = 3 to estimate the average velocity v valve = |:| \"x mm (b) At what time t (in s) was the instantaneous velocity equal to the average velocity? (Round your answer to one decimal place.) ave (in km/h) of the car during the first 12 seconds