Ok, we are going to calculate the volumes of the cans by separate, and next we are going to subtract them.
The volume formula is:
Volume of first can:
Diameter: 3.5
Remeber that the radius is the half of diameter.
Radius: 1.75
Height: 1.25
Volume of second can:
Radius: 1.2
Height: 1.25
Now subtract them.