Data Sufficiency

Last year the average salary of the 10 employees of company x was $42,800. What is the average salary of the same 10 employees this year?

a) For 8 of the 10 employees, this year's salary is 15 percent greater than last year's salary.

b) For 2 of the 10 employees, this year's salary is the same as last year's salary.

neither of the statement is not sufficient alone.

combining ,let 8 employee had salary 100x last year and 2 had 100y last year

so average 800x+200y/10=80x+20y=42800
or 4x+y=2140

this year average is (115*8) x+200y/10=920x+200y/10=92x+20y=23(4x+y)-3y

unless we know y average cannot be calculated.
hence ans E