Subject: mathqa
Question: bag a contains red , white and blue marbles such that the red to white marble ratio is 1 : 3 and the white to blue marble ratio is 2 : 3 . bag b contains red and white marbles in the ratio of 1 : 4 . together , the two bags contain 42 white marbles . how many red marbles could be in bag a ?
Option: 
A: 4
B: 1
C: 10
D: 12
Answer: C