I wanted to know if someone has a lot of qaza namaz since puberty, like combining all five, close to 30,000 according to rough estimates, what are the ways of clearing this number. Same goes for fasting.

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You have to make qaza of all the prayers and fasting you are sure you missed, so if you are confident that you missed 30000 prayers, then you have to make qaza of this number. However, if the number fluctuates between two like 25000 and 30000, you can choose the lower number, or something in between. The same thing applies to fasting.