÷2
i keep getting 7.26, but the answer is 3.0g/cm^3 what am i doing wrong?
: <

(45.82g / 3 cc - .64g / .859) / 2

(15.2733333333  - 0.7450523865) / 2

14.5282809468 / 2

and I get
7.2641404734

I'd say make sure all those numbers you posted (45.82; 3.0, etc) are correct.
Also, going by the units you have listed, the answer CAN'T be in 1/cm^3 units because the units should cancel and you'd have a dimensionless number.