Astore display rotates 40 times every half hour. how many times will the display rotate in 4 hours?

A store display rotates 40 times every half hour i.e 30 minutes
Thus, by simple calcultion, we say,
Therefore, the store display rotates 80 times in 1 hour i.e. 60 minutes
Now, 
Thus, the strore display will rotate 80*4 = 320 times in 4 hours

therefore, the answer is 320 times in 4 hours