The percentage of the same population with brown eyes and black hair is larger than the percentage of the sample population with blue eyes and black hair by

18

Step-by-step explanation:

There are 64 people with brown eyes and black hair out of 303 total people; this is 64/303 = 0.211 = 21.1%.

There are 9 people with blue eyes and black hair out of 303 total people; this is 9/303 = 0.0297 = 2.97%.

This is a difference of 21.1-2.97 = 18.13, or 18%.