Greetings!
1)
As stated,
, so if you plug all the values in: 100ml volume and 0.196g:
= 0.00196
2)
First, you need to find the total volume of the wood. If it has a width of 3cm on each side this means its a cuboid. The formula for the volume of a cuboid is:

Where in this case x = 3:
= 27, so the volume is 27.
Now we know the volume and mass so we can simply divide the two:
= 1, so the density is 1g/cm

Hope this helps!