Derek's total income for 2020-21 is £68,310 (entirely non-savings) and he makes a gross deductible payment of £3,000 in the year. He is not a Scottish taxpayer and he makes no Gift Aid donations or pension contributions. Show his income tax computation:

(a) with the deductible payment

(b) as it would have been without the payment.

How much has the payment effectively cost him? How much would it have cost him if his total income for the year had been £168,310? And in what ways would the situation have differed if his total income for the year had been £115,000?