If the average person can climb 7 stairs every 10 seconds, taking a 60 second break after each time they have climbed 455 stairs, how long in hours would it take to climb all the stairs in Burj Khalifa?

The volume of a spherical hot air balloon v(r) = 4 3 ? r3 changes as its radius changes. the radius is a function of time given by r(t) = 3t. find the instantaneous rate of change of the volume with respect to t at t = 2.