We can rewrite 3:4 as 3x:4x since we don't know the actual individual numbers, solely that it is divisible by these numbers.
Next, since we know 3x = 36 because of the question, we can solve for x using the division property of equality and get x=12. Once we have x=12 we can find the number of books the other trader has - 4x - by simply multiplying 12 by 4 to get 48 books. Now all we need to do is find the total number of books that both traders have and to do this all we need to do is add 36 to 48 to get a final answer of 84 books.
In an hour there are 60 minutes to find the unit rate of problems per minute you divide 60/24 and get 2.5 multiply 2.5 by 72 get 180 in minutes that is 3 hours
