Reoccuring data

Hello all, have a question about some re-occuring data generated from a formula
for example
i need to manually input some data into B21 and C20 and a answer in c21... heres the formula $B21+$C20 because i copied and pasted it down beacuse the numbers will change daily according to performance... my question is how can i fix the formula to where it wont automatically populate in C22,C23,C24 and so on until i manually input the numbers ...See attached for an example...
Thanks for your timeBook1.xlsx

If you look at the sheet, all i want to do is not have the formula in colum C and E auto populate until i manually enter the data that I need to input..

Formula:

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Past this into C22 and drag up and down. this will do the trick

Formula:

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and you can put this into G22 to fix that column

Perfect...Works fantastic. Thank you very much