\(k-kilo=1,000\ times\ more\ of\ some\ unit\\m-meter\\h-hecto-100\ times\ more\ of\ some\ unit\\--------------------------\\1km=1,000\times1m=1,000m\\1hm=100\times1m=100m\\\\together:\\5.5km+300m+23hm\\=5.5\cdot1,000m+300m+23\cdot100m\\=5,500m+300m+2,300m\\=8,100m\\\\because\ 1km=1,000m\ therefore\ 1m=0.001km\)
\(\boxed{8,100m=8,100\cdot0.001km=\boxed{8,1km}}\)