The graph of the velocity in km h of a car that is accelerating is shown in the figure where t is measured in seconds v km h Vave 60 40 20 6 12 i a Use the midpoint rule with n 3 to estimate the average velocity va in km h of the car during the first 18 seconds ave km h 18 S t seconds b At what time t in s was the instantaneous velocity equal to the average velocity Round your answer to one decimal place t