When Lila watches the video at twice the normal speed, the video takes 100/2 = <<100/2=50>>50 hours.
When she watches six such videos, the total number of video hours becomes 50*6 = <<50*6=300>>300 hours.
Roger, her friend, watches 6 videos at the normal speed, which is 6*100 = <<6*100=600>>600 video hours.
The total number of hours watched by the two is 600+300 = <<600+300=900>>900 hours.
#### 900