The correct answer depends on several factors, depending on how you store & get the data & if you intend to use sub reports or formulas etc
For instance, you could use a stored procedure that exposes the data to the report & requires the Start & End Date & Account identifier as parameters. In this case you could include the opening balance in the result data repeated on each data row & use a formula variable to calculate the closing balance for each line & overall - Crystal Reports cannot not see multiple tables in a Stored Procedure output.
Another option is to use Views in your DB & use these to get your opening & closing balances & transactions.
Alternatively you could use sub reports that get the closing and opening balance & then calculate each line.
How you do it is up to you.
The following link contains Crystal Reports Samples & should assist you;
SAP Crystal Reports Samples[
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Kind Regards