Conversion of mm to km
1km=1000m
1m=100cm
1cm=10mm
1km=1000000mm
So,
1mm=1/1000000km
76.3mm= 0.0000763km
Conversion of year to hours
1 year=12 months
1 month=7*31+5*30 days
1 day =24 hours
So,
1 year= 8760 hours.
Therefore the speed is
0.0000763km/8760hours
0.000000008710046km/h