Answer:
x=12
Explanation:
Since b would equal E
We can make an equation.
x^2 -5x = 84
So that can be solved down to
x^2 -5x -84= 0
(x-12)(x+7)=0
x=12
x=-7
Now we see which one equals 84.
(12)^2 -5(12)=84
-7^2-5(-7)=14
therefore 12 is the correct answer and -7 does not work.