Excel Formula - HELP!

[Jolyonekenobi]

Hello all

Am really stuck and would appreciate some help!!

I'm setting up a reporting sheet for my good lady's accounts and need some help with what should be a pretty straight forward Excel problem (if you know the answer).

I want to show a weekly income figure, calculated using the formula below. No problem there. How can I get excel to realise that C needs to increase by 7 on each subsequent line - surely I don't need to calculate this manually and type it in to every cell!!!

=SUM(October!C3:C7)
=SUM(October!C10:C14)
=SUM(October!C17:C21)
=SUM(October!C24:C28)

Can anyone please tell me what I can do to get Excel to autofill the rest of the column with the sequential formula!??!

Does any of that make sense?!

Please help!