On the bus, the number of Dutch people was 3/5 of the total number, a total of 3/5*90 = <<3/5*90=54>>54 people.
Out of the 54 people who were Dutch, 1/2 were Dutch Americans, a total of 1/2*54 = <<1/2*54=27>>27 people.
If 1/3 of the passengers on the bus identifying as Dutch Americans sat at the windows, their number is 1/3*27 = <<1/3*27=9>>9
#### 9