The question is looking at the people with a two year degree.
Find the total of people with a two year degree:
17 + 28 + 16 = 61 total.
Now they want the relative frequency for urban people.
Divide the number of urban people with a two year degree by the total people with a two year degree:
17 / 61 = 0.27868 x 100 = 27.87%