First we need to determine the volume of the glass
The glass is a cylinder
V = pi r^2 h
We have the diameter so we need to find the radius
r = d/2 = 3/2 = 1.5
V = pi ( 1.5)^2 ( 6)
V = 13.5 pi in ^3
We are putting in 3 ice cubes
The volume of one ice cube is
V = s^3
V = 1.5 ^3
V =3.375
Multiply by 3
3 * 3.375 = 10.125 in^3
We need to subtract the ice cube volume from the total volume
13.5 pi - 10.125
We need (13.5 pi - 10.126) in^3 of water