In order to properly measure the displacement, the object must be completely submerged, however in the diagram the wood is floating. So the measured displacement will only be a fraction of what it actually is.
They often create data tables, charts, or graphs to easily communicate results.
Answer:
The elements in group 13 and group 15 form a cation with a -3 charge each.
In every molecule of

there is 8 atoms of Carbon.
IF we have 3.7 moles of

to find the number of moles of Carbon, just multiply by 8
3.7 * 8 = 29.6 mol Carbon