A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Could you be more specific, as to get result of 150, we have to just multiply the membership cost ($50) to the number entered by you which is 3.
So may be you can set up a table, where column 1 have the membership fee and column B will contain number of members and in column C just multiply like A2*B2, then you can do the sum of column C.
For getting the result of 50000, you may use 'goal seek'.