A cone has a radius of 5ft and a height of 18ft if the radius of the cone tripled what is the new height of the cone

Question

A cone has a radius of 5ft and height of 18ft if the radius of the cone tripled what will be the new height of the cone. The volume of the stays the same 

Answer 1

V=(1/3)∏r²h

V=(1/3)∏5²18

V=(1/3)∏*25*18

V=∏*25*6

V=150∏

V=(1/3)∏15²h

150∏=(1/3)∏*225h

150∏=75∏h, so h must be 2 feet

another way to look at the problem...

V=(1/3)∏5²18

V=(1/3)∏15²h

V=(1/3)∏(3*5)²h

V=(1/3)∏5²*3²h

V=(1/3)∏5²*9h

compare the last equation with the first equation and you see that 18=9h, so h=2 feet