It was 3hexagons + 1 pentagon connected to each other, hence 17 carbons.
The first diagram showed a hexagon/pentagon dont remember with each carbon having 2 hydrogen bonds.
Hence you just types 17 by 2= 34, then minus the carbons which are used to connect the hexagons/pentagon , being 6 of them, hence they only have 1 carbon bond, hence its 34-6=28.
C17h28.
Thats what i got.