A savings sequence with explicit assumptions

For a school mathematics exercise, a student deposits 10 units at the end of the first week and increases the weekly deposit by 3 units each week. The exercise runs for eight weeks and assumes no interest, fees or missed deposits. A worksheet has separate boxes for the eighth deposit and the total deposited over all eight weeks. One student writes the same answer in both boxes because both questions mention eight weeks. Another counts eight increases after the initial deposit. The teacher asks for a method that can be checked by writing the first few terms. The currency unit is deliberately hypothetical and the exercise does not describe an actual savings product or any Korean tax rule.