remember
area=pir^2
circumference=2pir
the surface aera if you thinkg about it is
2 times the tops+area around
the tops are circles so 2*pir^2 is tops
the area around is a rectangle that has been wrapped around the cylinder,
the hieght is the legnth and the circumference is width
so 2hpir is the area around
2pir^2 is the areas of the tops
2hpir is the area around