Balance as per passbook means that we have write the first statement by looking this . 

For Example - If it is said that Dr. balance as per passbook , that means write the amount in Minus side because Passbook's Unfavourable balance is Dr. 

Similarly  in the case of balance as per cashbook.

For Example - It is said that Dr. balance as  per cashbook , we have to enter the amount in Plus side because Cashbook's favourable balance is Dr.

More Info :- 

Cash book = = =
-  Dr. - Favourable Balance 
-  Cr. - Unfavourable Balance 

Passbook = = =
- Dr. - Unfavourable Balance.
- Cr. - Favourable Balance

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By the way , I m too A Commerce Student
Mark my best , if you like my answer.
(1) credit balance as per passbook means bank balance & debit balance means bank overdraft.
(2) debit balance as per cashbook means bank balance & credit balance means bank overdraft.