https://www.beatthegmat.com/gmatprep-m-z-0-t25999.html

Another approach when statements are combined would be

m> 3z
4z>m

therefore 4z>3z which implies z>0(z is positive)

Since m>3z m must also be positive
m+z > 0 -> YES

Choose C

I used the following reasoning and got to a diff answer.

a. m-3z>0
b. 4z-m>0

combining both
m>3z
and 4z>m

thus 3z<m<4z.

Thus m can be any value between 3z and 4z. Lets assume 3.5z.
So, m+z = 3.5 z + z = 4.5 z

Now, as we dont know anything about z, whether it is positive, negative or zero, we can't answer the question.
So, E.

Please point out any flaw in my reasoning.