How many right angles do you need to add to get a straight angle?
__
Two right angles = 90∘ + 90∘ = 180∘ = Straight angle.
How many right angles do you need to add, to get a straight angle?
How many right angles do you need to add to get a 360 degrees?
How many right angles do you need to add to get an angle which is equal to angle around a point?