hello from mrbilldoesmath!
answer:
25x^2 + 90x + 84
discussion:
mn(x) = m(n(x)) = m( 5x + 9) =
(5x + 9)^2 + 3 =>
25x^2 + 90x + 9^2 + 3 =
25x^2 + 90x + 84 (as 9^2 = 9*9 = 81)
which is the second choice
regards,
mrb
p.s. i'll be on vacation from friday, dec 22 to jan 2, 2019. have a great new year!