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Take the like kinds and group them together (ie. A is apples and k is kangaroos)and add them. For your question you would get

(4a + 9a) + (+5k + 3k) + (-2)

Which then becomes
13a +...

Thanks Speedball. Changing the fitting to a male worked. I assume this is because the copper expands when the hot water flows through the joint so now the joint tightens inside the PVC when used...

I have a fitting in a wall which began leaking with mold developing on the wall board. When I took out the wall the culprit was a fitting between a female threaded copper fitting and a male PVC...