Start with a proportion, to get the number of degrees in 30 seconds:
(150 degrees / 5 seconds) = ('D' degrees / 30 seconds) .
Cross multiply the proportion: (150 x 30) = 5 x D
4,500 = 5 x D
Divide each side by 5 : 900 = D
The globe turns 900 degrees in 30 seconds.
How many rotations is that ?
Each rotation is 360 degrees.
So 900 degrees is
(900 / 360) = 2.5 rotations in 30 seconds.
