orbits

there are several tricky Mensa problems involving highly idealised, regular speed concentric circle orbits











here is a selection:
two planets and the sun are initially in line
the planets circle the sun, clockwise, at different rates

when are they next in line if they circle the sun:
1]  A: every 2 years    B: every 6 years?
2]  A: every 5 years    B: every 15 years?
3]  A: every 20 years  B: every 100 years?


 for a given ratio, it can be helpful to think about the angle turned by the faster planet when the slower planet goes through a particular angle

in general...?