x/110 = (320-x)/90
  Cross multiply
 90x = 35200-110x
 200x=35200
 X = 35200/200 = 176 (distance traveled by train going 110 mph
 176/110 = 1.6 hours = 1 hour and 36 minutes
  
 Check: 110*1.6 = 176, 90*1.6 = 144
 176+144 = 320
 it will take 1.6 hours ( 1 hour 36 minutes) for the trains to meet