1/50 of a mile is the distance the snail goes in 50 minutes. To get an hour, the snail must move for another 10 minutes (60-50=10).
Dividing 1/50 mile by 5 gives us 0.2/50 mile, which would be what the snail travels in 10 mins.
This can be added to 1/50 to give 1.2/50 mile as the answer
OR
You can take 0.2 and times it by 6 (to get 60 minutes from 10 minutes) to give the same answer as above.
Either way, the snail has gone 1.2 miles after the hour has passed.