Solution: Let x be the total space of hard drive.
We are given 80% space of hard drive is full and 12000 megabytes are free.
We can write:





megabytes
We have to free 5% of space as the difference between 80% and 75% is 5%.
Therefore 5% of 60000 is:

We know that 1 minute of video uses 60 megabytes of space.
Therefore number of minutes of video that should be deleted to make 75% of space free is:
minutes of video
Hence, 50 minutes of video should be deleted so that the hard drive is 75% full.