I think you mean that the polygon goes to the next side every minute,
and makes a complete rotation every hour.
So each minute, it advances by 1/60 of a complete rotation.
A complete rotation is, of course, 360° .
So each minute, it advances (360°/60) = 6° .
In 7 minutes, then, it advances
(6° / minute) x (7 minutes) = 42° .