2. The altitude of a rock climber t hours after she begins her ascent up a mountain is modelled by the function a(t) = -10t'+60t, where a(t) is the altitude, measured in metres. a) Use limits to determine the average rate of change of the altitude of the rock climber at time t. Express the derivative using Leibniz notation. 13 b) Determine the rate of change of the altitude of the rock climber of the javel after 3s. A_ 12