the magnitude of a right angle is 90°.
we are asked to find a fraction of 90°.
one sixth as a fraction is 1/6.
therefore to find 1/6th of a right angle we can calculate as follows
1/6 of 90
when we have the 'of' function it means to multiply

numerators are multiplied by numerators and denominators multiplied by denominators

angle is 15°
therefore 1/6th of right angle is 15°