Determine whether the statement is sometimes , always, or never true if ax + b - 4 =b and a = 0 then x = 4/a

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.