Dimensions of the glasses: Diameter, d = 3 in; depth, h = 6 in
Volume of 1 glass = (πd^2/4)*h = (π*3^2/4)*6 = 42.41 in^3
Each of the three guests will be served a glass full of milk.
Volume of milk required = 3*volume of 1 glass = 3*42.41 = 127.23 in^3
But,
1 in^3 = 0.0163871 liters
Therefore,
127.23 in^3 = 127.23*0.0163871 ≈ 2.09 liters will be required.