Answer:
3km = 3000000 milimeters = 3000000mm
Step-by-step explanation:
1 km = 1000 meters
1 meter = 1000 milimeters
then:
1km = 1000*1000 = 100000 milimiters = 1000000mm
3km = 3*1000000 = 3000000 milimeters
