Optimization calculus problem

i understood that area= sa of hemisphere+ la of cyclinder and volume is volume of hemisphere + volume of a cyclinder

cost equation is c(8) = 2pi radius squared plus 2pi radius times height

and volume for h is (6000 divided by pi times radius squared )minus 2r divided by 3

my question is how did c = 12000 divided by r plus 44pi r squared divided by 3 come about? or basically how did they get that c?