the correct answer is C: 28%
to solve you have to subtract the amount of change, so 2700-2100= 600
then you take 600 divide by the original number which is 2100. so your equation is change divided by original, or in this case 600/2100, when you divide the equation you get an answer of 0.28, you then have to move the decimal 2 places to the right, to get an answer of 28%
hope this helped! :)