David has a collection of computer games. last year, he had 400 cds in his collection and this year he has 120% as many cds as he had last year. what is the size of his cd collection this year?

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.