@Bryce these concepts are discussed in our Sufficient & Necessary lesson and in our Strengthen with Sufficient Premise discussion from the Strengthen lesson.
Let's try a missing premise drill together to see if it helps:
P: B ==> Not X
P: ?
P: Not A ==> Z
C: Not Z ==> Not X
Okay so first these are Strengthen with Sufficient Premise questions in the abstract.
The idea is there is a gap in the argument and we are looking for the answer choice that would make the conclusion follow logically.
Notice the sufficient condition of your conclusion is "not Z" so that is where I will start.
Contrapositive of P3 is Not Z ==> A
So we have A but then we are stuck because A is not a sufficient condition of any of our premises.
So the jump here clearly will relate to A.
We are trying to get to "Not X" because that is your necessary condition of the conclusion.
P1 gives us "Not X" because "B ==> Not X"
So if we can connect A to B we would complete this argument logically as follows:
not Z ==> A ==> B ==> not X
So the missing premise is A ==> B.
Hope that helps! Please let us know if you have any other questions.
