Answer
About 2.25 GB. In review, anything from 1.13 to 4.5 counts as right.
The worked estimate
5 Mbit/s ÷ 8 = 0.625 MB/s. × 3,600 s = 2,250 MB ≈ 2.25 GB. Video services store several resolutions of each video, so the total is a few times that.
Numbers: Numbers to know.