this is my question:
calculate the volume of a piece of wood which weighs 102g and has a density of 0.85g/cm^3?
would i do 0.85 x 102 =86.7 cm^3?
Think about your units. They will save you.
By multiplying the two given values, your units are $\displaystyle \frac{gm^{2}}{cm^{3}}$. Does that look like volume to you?
If you divide the mass by the density, you get $\displaystyle \frac{gm}{\frac{gm}{cm^3}}\;=\;cm^{3}$. Does that look like volume?
Additionally, you should seek clarity from the definitions. What is the definition of density? Find it in your book. Mass/Volume? Something like that? Well, if you have Density = Mass/Volume and you are given Mass and Density, you are left with only a small algebra problem. Substitute and solve.
Note: Make sure you know the difference between Weight and Mass. They are NOT the same thing.