The correct sentence is "bohat (very) achay (good), kaun (who) tumhain (you) hindi sikha raha(teaching hindi) hai (is/present form) "bohat achay, kaun tumhain hindi sikha raha hai?" Means "very good, who is teaching you Hindi?" And to answer the question in Hindi you'll say: mujhay (me) Septi(anyone's name:e.g yours) Hindi sekha rahi hai(is teaching). "mujhay Septi Hindi sekha rahi hai" Means " Septi is teaching me Hindi" Thing to remember: for female we use: sekha rahi hai. and for male we use: sekha raha hai. (just the way we use him/her, his/her, he/she in english so there are such rules in Hindi also.

Sorry i think this is not correct sentence. So here i would like to make guess, Might be he/she was saying "Bahut acha , kaun tumko hindi sikha raha he?" Means "Very good ,who is teaching you hindi'? Now i think you know what to answer.(if my guess is right) Have a nice day!!

It means very good who is teaching you Hindi

I think somebody asked you this question who knows hindi very well , if you got this sentence during chating with hindi person then correct sentence should be" tumhara hindi bahut acha hai , kisne tumhe sikhaya?" "your hindi is very good....who taught you? " and then you can answer him/her " mai khud se sikhti hun" i learn it by myself.

It means Very good.........Who teaches you hindi? this is simple present tense. so you've got write in hindi in simple present tense too: Bahut acha.......Kaun tumhe hindi sikhta hai? or Bahut acha.......Tumhe hindi kaun sikhata hai? both mean exactly the same.