The question isn't clear enough, I think it ask us to calculate the linear speed of a point at the edge of the DVD.
Now let's imagine we're a point at the edge of the DVD, we're undergoing a circular motion. Each minute we will complete a circular track 7200 times, now we need to know the distance we travel each turn. The perimeter of the DVD, a circular object is:
[tex]P=2\pi.R[/tex]
Know recall that:
[tex]v=\frac{d}{t}[/tex]
We now need to know how much distance is traveled during a minute or 60 seconds:
[tex]D=7200\times 2\pi\times R[/tex]
Finally we divide this result with t=60 seconds:
[tex]v=\frac{7200\times2\pi\times R}{60}
\\
R=\frac{12}{2}=6
[/tex]
[tex]v\approx 4523.89 \frac{units}{second}[/tex]
Where the distance units were named units as the length unit is not specified in this exercise.
