12 km in 4 hours means 3 km in 1 hour, so it must take 3 and 1/3 hours to go 10 km. 1 hour is 60 minutes so 3 hours is 180 minutes plus 1/3 hour is 20 minutes, altogether 200 minutes.
John
Egw to Beta kai to Sigma
My calculator said it, I believe it, that settles it