Answer
If the number of colas per week increases by 1, it is expected that the bone density will decrease by $0.002889~g/cm^3$ (increase by $-0.002889~g/cm^3$).
Work Step by Step
We could also have said that when the number of colas per week increases by 1, the bone density decreases by $0.002889~g/cm^3$, on average.
