If you do 30 push-ups three times a week how long will it be to see results?

instead of doing 30 push-ups try to do 4 sets till failure. and switch different push-ups exercises every week, so lets say the first week you do Diamond push-ups, next week wide grip push-ups, the week after normal push-ups and after that Knuckle push-ups. after a few weeks try to do 2 or 3 push-ups exercises till failure and so on, try to keep changing your routine. Make sure to rest enough, so 3 times a week is good if you have 1 day of rest in between, don't forget to eat good too! you should be seeing results in no time :)