The sum of a number and 6 ad a mathematical expression

55 copies

Step-by-step explanation: Knowing that the total for all 3 classes is 135 and 25 less copies were made for the 1st class than the 2nd and 3rd combined, we have to figure out how much copies were made combined for the 2nd and 3rd class first. Then, after finding that combined number for the 2nd and 3rd class, we'd subtract by 25. Since the number has to be combined for the 2nd and 3rd class, it'd make sense for the individual copies to be the same. After playing around with numbers, a number that happened to fit the description was 40 copies. By multiplying this by 2, you get 80 copies which is the combined copies for tthe 2nd and 3rd class. Next, you would subtract 80 by 25, which represents the 25 less copies made for the 1st class. You end up with 55 copies. Finally, to check your answer, add 40, 40, and 55, which equals to 135.

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