Answer:
28%
Explanation:
Intuitively, we can figure out that 140 is the amount we need to markup by.
We know that 140 is 28% of 500, and therefore we can conclude that the markup is 28%. We may check our answer by multiplying 500 by 128%, or 1.28, which yields the result of 640. By the "definition" of what a markup is, the markup will only be 28%, not 128%, since it implies that you are already withholding the original cost, just adding more.