Rent received

If that is all you are given then you cannot calculate either the cash received or the rental income - you need one of them to be able to calculate the other. Best is to write up a t-account in exactly the same way as we do for for expenses when there are accruals and prepayments. When it is income as with rent received, the rent received in advance is a credit balance (because the tenant has overpaid) and rent received in arrears is a debt balance (because the tenant is still owing us money).

Yes sorry I forgot to mention that rent received is mentioned in the question but I don't understand how to calculate the missing figure when there are closing balances on both sides. I mean the figure that has to be included in the SOPL.

The rent received is credited to the rent account (and debited to cash), and the missing figure is the rental income to appear in the SOPL.

I understand that but I don't understand how to find the value of rental income that will appear in the SOPL. I set up the t accounts and balances correctly but I don't understand what to do after that since there are closing balances on both the debit and credit sides

As I replied before, the missing figure on the account is the figure to appear in the SOPL.