I want to quit part-time job

I do two part time job now. One of two is wedding hall staff and the other is drug store staff. I should go drug store more than 15 times a month, and the shop close at 0 o'clock, then I can go home 0:30 to 1 o'clock. It is very hard. In  addition, I have to do KGU many homework. If it be the same condition from now on, I will fall credits, so I want to quit the part time job, and I want have time, but I can't tell it to manager, because I hate to think what could happen, but I think should say it.

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