Dorothy's income tax and Class 4 NICs liability for 2020-21 was £24,600, of which £600 was deducted at source. Her liability for 2021-22 is £28,000, of which none is deducted at source. She made a first POA in respect of 2021-22 on 27 February 2022 and a second POA on 12 September 2022. She also made a balancing payment for the year on 21 February 2023. All of her payments were for the correct amount. 

(a) Calculate the late payment penalties payable by Dorothy in relation to 2021-22. 

(b) Assuming an interest rate of 2.6% per annum, calculate the amount of any interest payable by Dorothy in relation to 2021-22.