budget sheet formula

a novice here
i am in need a formula for a debt management budget sheet i am working on.
im looking to make it as automated as possible.
so i am looking for the user to input a figure in box one
and get a calendar month figure in box three
so in box two it will need to be a drop down of weekly, monthly, or annually of how the credit/debt is come by.

when they check the relevant frequency from a drop down it will then have a formula to work out the relevant maths.

can anyone help with this or know to a template i could use as reference?

all help gladly received.