Given that in the alien planet the names of substances and the units in which they are measured in not familiar.
8 quibs of a substance called skvarnik is present.
The conversion factor between sleps and quibs is: 9 sleps = 13 quibs
Converting 8 quibs of skvarnick to sleps:

5.54 when rounded to nearest tenth becomes 5.5.
So the correct answer would be 5.5