Given:total salary= $42,800*10.
Question:new total salary=?
As you already know that each statement alone is not sufficient.
When taken together.Consider two possible cases:
2 lowest salaries didn't change and 8 highest salaries increased by 15%;
2 highest salaries didn't change and 8 lowest salaries increased by 15%;
Ask yourself,would new total salary be the same for both cases?No,because increase in amount for the first case will be more than increase in amount for the second case.Hence even taken together statements are not sufficient.
Answer:E.
Hope it's clear.