The third calculation, namely "P(VERB | PROPN) P(drew | VERB) = 2/4 2/6 = 3/12" should instead use 3/6 instead of 2/6 as the probability for P(drew | VERB), as can be seen on the previous slide and the probabilities in the image below, making the answer 1/2, not 3/12.
Also (just because I noticed), the answer for the third calculation as it is written currently should match the fourth calculation, since they use the same values, so should be 2/12, though this is obviously irrelevant since the third uses incorrect values.
The third calculation, namely "P(VERB | PROPN) P(drew | VERB) = 2/4 2/6 = 3/12" should instead use 3/6 instead of 2/6 as the probability for P(drew | VERB), as can be seen on the previous slide and the probabilities in the image below, making the answer 1/2, not 3/12.
Also (just because I noticed), the answer for the third calculation as it is written currently should match the fourth calculation, since they use the same values, so should be 2/12, though this is obviously irrelevant since the third uses incorrect values.