The task is to generate the correct answer for a given math problem.

Problem: 5 years ago , paula was 3 times as old as karl . in 6 years , paula will be twice as old as karl . what is the sum of their ages now ?
54

Problem: after decreasing 24 % in the price of an article costs rs . 684 . find the actual cost of an article ?
900

Problem: a tourist does not have to pay tax on the first $ 600 of goods he purchases in country b , but does have to pay a 7 percent tax on the portion of the total value that is in excess of $ 600 . what tax must be paid by a tourist if he buys goods with a total value of $ 1720 ?

$ 78.40