Consider the volume of the region shown below, which shows a right circular cone with top radius 3 cm and height 10 cm. we have used the notation dy for \delta y

I have the same problem here with a slight change in the given values:

radius is 2 & height of 6 indicates the bounding line is y = 3 x---> x = y / 3 

thus the [ π radius ² thickness ] yields π (y² / 9 ) dy , y in [ 0 , 6 ] for the volume... 

a Riemann sum is then : y_i = 0 + i [ 6 / n ] = 6 i / n , i = 1,2,3...n and do a right side sum 

π Σ { i = 1,2,3..n } [ 36 i² / 9 n² ] [ 6 / n ]

I hope my guide has come to your help. God bless and have a nice day ahead!