posted by coried .
The surface area of a balloon is given by S(r) = 4(pie)r^2, where r is the radius of the balloon. If the radius is increasing with time t, as the balloon is being blown up, according to the formula r(t)=4/5t^3,t>=0, find the surface area S as a function of the time t.
r= 4/5 t^3
S=4PI (4/5 t^3)^2 and then you simplify that.