First find how long Milly spends studying geography by dividing her math homework time by 2: 60 minutes / 2 = <<60/2=30>>30 minutes.
Now find the total amount of time Milly spent on math and geography: 30 minutes + 60 minutes = <<30+60=90>>90 minutes.
Now calculate the mean amount of time Milly spends on math and geography by dividing the total time spent by the number of subjects, which is 2: 90 minutes / 2 = <<90/2=45>>45 minutes.
Now add the time Milly spent on all three subjects to find the total: 45 minutes + 30 minutes + 60 minutes = <<45+30+60=135>>135 minutes.
#### 135