help me please!!! chem lab how do you find.....

ok so i did a lab and it's asking to write down the volume to mass ratio... but i have the two masses.. one of the whole tablet of alka-seltzer and the mass of a piece of the tablet. then i have the volume.. but do i like add those two together and get the total mass then make it into a ratio?? help!

here's my data:
Whole tablet(1st column) Piece of Tablet(2nd) Volume (3rd)
1. 3.23g 1. 0.50g 1. 3.7 mL
2. 3.23g 2. 0.82g 2. 9.7 mL
3.2.50g 3. 2.50g 3. 37.2 mL
4.3.23g 4. 3.23g 4. 42.6 mL

thanks! =]