3y 12 What constellation?

It's actually quite simple. The time for two snails to meet is 12 minutes (that is to say, the distance for snails to climb together is 12 minutes), and the time ratio is 3:4. So the ratio of a to b is 4/4 3. The ratio of b to b is 3/4 3. So the time of b is 12/3/4 3=28. A takes 12/4/4 3=2 1, and the subtraction answer is 7. Ha ha, this is the simplest method, how, easy to understand!