1 hour is 60 minutes so 3 hours is 3*60 = <<3*60=180>>180 minutes
Three-quarters of 180 minutes is (3/4)*180 = <<(3/4)*180=135>>135 minutes
He spends 15 minutes on 1 page so he will spend 135 minutes on 135/15 = <<135/15=9>>9 pages
#### 9