You need to work this problem backwards. If he caught 30 fish, which was six more than twice the number he caught last year, you would start by subtracting six, leaving you with 24. Then you'd have to divide by 2, because it was twice plus six as many fish, which would give you 12 fish.
Each dvd cost $7.50 how? Your friends buy 8 dvd's and in total is 60, you want to divide 60 from 8 and find that it's 7.50 and then multiply 8 to 7.50 and it should be 60. Hope this helps!!