9,6% is the ANNUAL interest
365 days = 1 year (not counting leap years)
23/365 = 0.063013698....
I = P R t = 4000 * 0.096 * 0.063014698....
= 24.20
you can also do 0.096/(12*30) <---12 months per year times 30 days per month (on average)
In that case, 4000 * 0.096/(12*30) * 23 = 24.53