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is m+z positive?
(1) m>3z
m=1, z=-2, => 1-2=neg
m=2 z=.5 => 2-.5=pos
insufficient.
(2) 4z>m
z=-1 m=-5 -5+-1=neg
z=1, m=.5 .5+1=pos
insufficient
1 and 2 combined, you get following inequality. 3z<m<4z. in order to satisfy this condition, z must be positive which in then makes m positive so m+z will be positive.
C
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