Noah’s bedroom light uses 6 watts per hour, so it would use 2 * 6 = <<6*2=12>>12 watts in two hours.
His office light uses 3 times as many watts as his bedroom light, so it uses 3 * 6 = <<3*6=18>>18 watts per hour.
In two hours, the office light would use 18 * 2 = <<18*2=36>>36 watts.
The living room light uses 4 times as many watts as his bedroom light, so it uses 4 * 6 = <<4*6=24>>24 watts per hour.
In two hours, the living room light would use 24 * 2 = <<24*2=48>>48 watts.
Thus, if Noah leaves all those lights on for two hours, he has used 12 + 36 + 48 = <<12+36+48=96>>96 watts.
#### 96