The tax owing is reduced by the tax on the purchases of 3,150.
Therefore, the net amount owing to the state is 4,112.5 – 3,150 = 962.5
As it is owing to the state, it is a liability and therefore a credit balance.
Do watch my free lectures on this – the lectures are a complete free course for Paper FA (F3) and cover everything needed to be able to pass the exam well.