Answer:
x3
Step-by-step explanation:
Considering x4 and x3 actually power terms.
I mean: x4 is
and x3 is
.
Let's decompose the first term: 
Now it is clear that the common factor is
.
You would write the expression as nP +nL=cost because it’s the number of plagues that he buys plus the number of loaches that he buys