If you just need the current balance, you could just do something like
=sum(income!C:C)-sum(expense!C:C), where income and expense are the worksheet
names and C is the column in which each amount is posted.
If you want to have the history of the balance at each day's end, you'll
probably change the SUM functions to SUMIFs, comparing the date on the
summary sheet to the dates on the income and expense sheets, getting each
day's change and adding it to the prior day's balance.
--Bruce