Barbara's liability to income tax and Class 4 NICs for tax year 2019-20 was £26,000, of which £4,000 was paid by deduction at source. Her liability for 2020-21 is £30,000, of which £1,000 has been deducted at source. State the dates on which Barbara is required to pay her 2020-21 liability and compute the amount payable on each date.

Ignore Class 2 NICs and capital gains tax.