Assuming that it's compound interest (i.e. interest is earned on the interest from previous years), your £24k would become £25,664.25 after 3 years. (i.e. that's £1,664.25 earned)
How exact do you need the figure to be? 1% pa is £240 in year 1 or £20 a month so 2.26% will be roughly £45 a month or £540pa. Over three years that would be £1620. Then add a little bit more - around £40- for interest in years 2 and 3 on your past interest.
If you need an exact figure there are sites that work it out for you if you have no pen/paper or calculator
eg https://www.thecalculatorsite.com/finance/calculators/savings-calculators.php