Selfstanding income

I've applied  already  2 times my wife visa was rejected because i can't prove my income so they are asking offenly & it was very low. Again i've applied now in Nov 4 . I'm selfstanding,i ‘ve my own business  & i can see in tax return 2017 my netto income as selfstanding is 20400 ( twenty thousand four hundred ). is this income is oke or not???. there is any chance they can reject again.?? please suggest me with a words ,, thank you

Minimal yearly gross salary with work card B is 41739 (as 13.94 payments). This amount is enough to get approved visas for whole family of four people (2 adults, 2 kids).

So I believe that such gross income would be for sure enough to get you approved wife's visa.