1. over 120 or make the top 2.5%.this means the cutoff score could be lower than 117.
2. the AMC people try to make A&B have same level of difficulty, but nobody knows which is easier, and it depends on individuals.
3. it is easier to make the AIME by the AMC12, since there are a few same problems on AMC10 and AMC12, and AMC12 has low cutoff. You can look for local universities or colleges see if any of them host the B test.