Complete 20km=------m
"kilo" means a thousand in Greek, so one kilo-meter is literately a thousand meters. (some people i know write "k" in slang for a thousand). so 20 km is 20 thousand meters, which is 20 000 m.
\(\sf 1~kilometer = 1,000 ~meters\\\\20~km= 20 \times 1000~m=\boxed {\sf20,000~m}\)
