I have a problem in finding the solution of problem. The problem is as follows:

Find the maximum value of yz + xz subject to the two constraints, y + 2z = 1, x + z = 3.

The answer in the textbook is 4/3. However, the answer I have is -(3/4)

Is my answer wrong? if wrong, how can I get to the answer 4/3?

Thank you very much