Explanation:
of course there is an explanation. and a correct answer (not just a wild guess).
f(x) = 2x
g(x) = 2x² - 1
f(g(x)) means that x is first processed by g, and then the result of that is processed by f.
in other words, the whole functional expression of g becomes the input argument for f.
therefore,
f(g(x) = 2(2x² - 1) = 4x² - 2
so, the correct answer is light blue.