5 because of two ways one you could do 6*what is 30. Or you could do repeated addition 30=5+5+5+5+5+5. But when you do 30=5-5-5-5-5-5. You are doing repeated subtraction which is equivalent to 30-5*6= 0.
The answer if 5 because because you can first divide 30 by 6 then get 5, and you can check that answer by subtracting 6 from 30, 5 times -hope this helps
