Deposit/Deferred Income question

Hi

I’m not sure if this is the right place to post this question from an audit test…

We are acting as agent for a client which tasks us with managing their publicity account.
They have an annual spend of £240,000 which started in Jan 2015 for 12 insertions, one per month on an equal basis.

We have received the following payments from the client:
1 Jan 15, 20% deposit on account – no invoice raised
1 Apr 15, 30% of total spend on account – no invoice raised

The only sales invoice raised in the year was 31 Mar 15 for £30,000

What balance would appear in the sales ledger & any provisions relating to income as at:
31 Jan 15
28 Feb 15
31 Mar 15
30 Apr 15

Does anyone know the answer? Thanks