how to solve simple andcompound interest

for the simple interest the percentage will not change at any time the interest will be same at every year
in case of compound interest it will differ year by year...
for example
interest for 1st year is 10% and interest for 2nd year is 10%
simple interest is 10% only
compound interest is 21% after the 2 years
compound interest we can caluclate by 1st year = x= 10%
2nd year = y= 10%
then compound interset for both years = x+y + (x*y)/100