Accruals and Prepayments

Hello

Could you please help me to understand the below question? Unfortunately I am not able to understand it even with the answer.
The Electricity account for the year ended 30 april 2005 was as follows:
Electricity accrued at 1 May 2004.
Payment made during the year in relation to

Quarter ending 30 June 2014 400
Quarter ending 30 Sept 2004 350
Quarter ending 31 December 2004 425
Quarter ending 31 March 2005 450

Which of the following is the appropriate entry for electricity?

Accred at 30 april 2005 150
Charge to income statement for year ended 30 april 2005 1525

below the Electricity T account

DR Bank 400 CR Balance B/F 250
DR bank 350 Income statemnet 1525
dr bank 425
dr bank 450
balance C/F 150

1775 1775

No problem with the Balance B/F of 250 as accrual from 2004, but I canno figure out where Balance C/F of 150 come from

Unfortunately the book does not provide any calculation.

Thanks a million

Gabbi