I chose E as well for this Q . However, my approach was as follows
Since we do not have information about individuals salary .. the $42,8000 can be split in any way ( ie . one person might have earned 20000, another person 3000 etc etc ) . Had the question mentioned about the individuals salary being the same.. the answer would have been different . Hence we cannot assume which individual got a raise and who did not ..
I have the same thought process Bunuel. Are we on right track ?
In others words we know that Total of 10 salary for Year 1 = 42800*10 = 428000. This is in no ways indicates that each employee had similar salary. it could be something like S(1) + S(2) .......S(10) = 428000. Here any of the 8 salaries could be increased by 15 % and any of the 2 could remain unchanged so finding the new average salary is impossible.