[M.B.E.]

Assume you start with 10K in chips. If you call this hand and lose you'll have 5K; then the probability of getting to 20K will be 0.6 x 0.6 = 0.36 (since you have to double through twice). I don't think that's exact but it should be a good approximation. If you call and win you'll have 15K; then your chance of reaching 20K might be something like 0.8. So we solve for this equation:

0.6 = 0.8p + 0.36(1-p)
0.24 = 0.44p
p = 0.545

So I'll say B.