V=pi*(r^2)*h (volume of a cylinder)

=3.14159*(50^2)*30, (30 is half of 60 and we fill the cylinder half full)

=3.14159*2500*30

=3.14159*75,000

=235,619.25 cubic cm

l liter=1000 ml and 1 ml=1 cubic cm

235,619.25/1000=235.61925 liters

the flow is 12.3 liters per minute

235.61925/12.3=19.156 minutes

answer: 19.156 minutes

By the way, why does l ml=1 cc ?

a liter is a cubic decimeter, a cube 1 dm by 1 dm by 1 dm or 10 cm by 10 cm by 10 cm whose volume is 10^3 or 1000 cubic cm

but a liter is 1000 ml, so 1000 ml=1000 cc, and therefore 1 ml=1cc (cc=cubic centimeter and

ml=milliliter)(also note that milli means 1/1000)