It would help if you proofread your questions before you posted them. I assume you mean "red marbles to blue marbles".
7:11 or 7/11
there are 11 blue marbles and seven red marbles in a box write the ratio of marbles to blue marbles
2 answers
on the other hand,
marbles : blue-marbles = 18:11
marbles : blue-marbles = 18:11