Let d=vt where v is constant (km/h), then 0.31=5.5v, v=0.31/5.5km/h. So d=(0.31/5.5)t.
When d=117, 117=(0.31/5.5)t, t=117(5.5/0.31)=2075.8h approx.
This can be done by simple direct proportion arithmetic.
t/d=5.5/0.31=t/117, t=117(5.5/0.31)=2075.8h.
If t=18d and t=5.5, 5.5=18d, d=5.5/18=11/36=0.3056 approx.