In a box, the ratio of red marbles to blue marbles is 7:4. Which of the following could be the total number of marbles in the box?

As the simplest form of the ratio is 7:4

Therefore the common factor of 7 and 4 can be taken as x.

Therefore total number of marbles is 7x+4x = 11x.

Therefore number of marbles in the box is a multiple of 11.
As 11x2 = 22

Therefore number of marbles = 22