1*2:2*4:3*5= 1:8:15. It's that easy!

To see why that works, look at specific times and days. If the first teacher spent one hour on the internet then the second teacher spent 2 hours and the third teacher spent 3 hours. If the first teacher spent 2 day on the internet then the second teacher spent 4 days and the third teacher spent 5 hours. The first teacher spent 1 hour per day for 2 days so 2 hours on the internet. The second teacher spent 2 hours per day for 4 hours so 8 hours on the internet. The third teacher spent 3 hours a day on the internet for 5 days so 15 days on the internet.