It is geometric because it is increasing by a common factor. If you multiply the previous number by 6 you receive the next number. If it were arithmetic you would add the number, not multiply.
Tenth: 243.9
Hundredth: 243.88
Ten: 240
Hundred: 200
The question says the machine uses up m gallons of oil each hour on weekends.
This means that if the machine works for 24 hours each day, it implies that:

There are only two days on weekends i.e. Saturday and Sunday.
This means that if the amount of oil used in 1 day in the weekend is 24m, then we can say:
Saturday: oil used is 24m
Sunday: oil used is 24m
Total oil used during the weekend is: