before we write the ratio, we have to figure out how many marbles we have in each pair. we can do this by simply adding. blue + yellow = 7 blue + 14 yellow = 21 marbles white + black = 1 white + 10 black = 11 marbles now, set up the ratio: blue + yellow : white + black 21 : 11 (also written as 21 to 11) so the answer would be c hope this helps!