im not sure where to post this

so

a bank loan of 500 pounds is arranged to be repaid in two years by equal monthly instalments. Interest, CALCULATED MONTHLY, is charged at 11% per annum on the remaining debt. Calculate the monthly repayment if the first repayment is to be made one month after the loan is granted.

I've been working for almost two hours on this problem, ending up with the equation (500-m)(1211/1200)^24 - (1200m/11) ((1211/1200)^24 -1)

m being the equal monthly repayment

from there i ended up with m= 21.something, apparently not far from the truth but nevertheless incorrect; can somebody show me how they would do this?