Turn 621/2% into a fraction in simplest form

An objects motion is described by the equation d= 4sin (pi t) what will the height of the object be at 1.75 seconds?

Math question.. plz me .. best answer all

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.