An increase in Y (of just the right amount) would restore equilibrium. Hence, each value of e is associated with a larger value of Y. OR, a decrease in NX of just the right amount would restore equilibrium at the initial value of Y. But the decrease in NX requires an increase in e. Hence, each value of Y is associated with a higher value of e.
Rationale: Doing this exercise now will break up your lecture, and will prepare students for the fiscal policy experiment that is coming up in just a few slides.