Obéir à – in French, you do not “obey someone” you “obey to someone” (or something). “J’obéis à la prof mais tu n’obéis pas à la prof.”
Réussir – it is always important to study how a verb is used in context and “réussir” is a perfect example of this. When you pass a test “vous réussissez à un examen.” If you manage to do something “vous réussissez à le faire.” However, for many things, you can use the verb without any extra little words added in. For example:
“She makes good cakes.” – “Elle réussit bien les gateaux.”
“He’s making a success of his life.” – “Il réussit sa vie.”
Novel French Learning 