So for this problem you know that 15 is 1/4 of an hour so to get the amount of papers each individual could deliver by themselves in an hour you would multiply the amount they can deliver in 15 minutes by 4. Denny delivers 6 so multiplying that by 4 is 24. Next Brendan delivers 5 in 15 minutes so multiplying that by 4 you get 20. The final step is to add 20 and 24 to get the total amount of papers between the two of them that gets delivered in an hour. This will result in your answer of 44.
