Answer: 
33.5% of commuters took public transportation in San Francisco.
Step-by-step explanation:
Let p be the percentage of commuters took public transportation in San Francisco.
Given: 53.4% of commuters took public transportation in New York City, which was 19.9% greater than the percentage in San Francisco.
That means,
53.4 = 19.9 + p
Hence, required equation : 
Subtract 19.9 from both sides , we get

hence, 33.5% of commuters took public transportation in San Francisco.