To estimate the slope of the tangent line at t = 15, we average the slopes of the adjacent secant lines for t = 10 and t = 20. As obtained in part (a), those slopes are msec = −148.8 and msec = −112.8, respectively. Therefore, the slope of the tangent line at t = 15 is as follows. (In the last step, round your answer to one decimal place.)
