a REALLY helpful thing when doing physics is something called the DMV triangle. So how it works is you look at what you are trying to find, which in this case is density. So you cover the D and look at the remaining M and V. Everything below the M has to be divided, and if you are just left with the D and V then you x them. It’s really simple and easy to use. So you cover up the D, and are left with M and V. So now you have to do Mass divided by Volume. 869g divided by 287cm3 would be 3.02g/cm3