BSTX practice assessment 2 task 6

Parki82

Adam has been trading for years his liability is as follows:
2015/16 £9600
2016/2017 £15450
2017/2018 £13500
Complete the total payments Adam will make
31st July 2018 - £7725
31st January 2019 -£4800
31st July 2019 -£6750

I’m really struggling how the answer arrived at 4800 for January 2019.
Please could someone explain to me?
Thanks

douglasstroud

In 17/18 his liability was £13,500 but he has already paid £15,450 in POA so he had paid £1,950 too much
His first POA in Jan 19 would be half of £13,500 which is £6,750 minus the overpaid £1,950 which makes £4,800