inequality
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The first statement reduces to m > 3z, which can definitely be satisfied by two positive numbers, and can definitely be satisfied by two negative numbers. Therefore, this statement is insufficient.
The second statement reduces to 4z > m, which can definitely be satisfied by two positive numbers, and can definitely be satisfied by two negative numbers. Therefore, this statement is insufficient.
Then consider both together: 3z<M<4z. If 3z<4z, then z must be positive since this would not hold for negative value of z. If z is positive, then 3z is also positive and if M is greater then 3z, then M is also positive. If M and z are positive, then m+z >0 must always be true and the answer is C.
The second statement reduces to 4z > m, which can definitely be satisfied by two positive numbers, and can definitely be satisfied by two negative numbers. Therefore, this statement is insufficient.
Then consider both together: 3z<M<4z. If 3z<4z, then z must be positive since this would not hold for negative value of z. If z is positive, then 3z is also positive and if M is greater then 3z, then M is also positive. If M and z are positive, then m+z >0 must always be true and the answer is C.