To express a compound length as a decimal in kilometres, convert the metre part to kilometres by dividing by 1000, then add.<br><br>
&bull; 30 m = 30 ÷ 1000 = 0.03 km<br>
&bull; 4 km + 0.03 km = 4.03 km<br><br>
Final Answer: 4.03 km