Answer:
Option C.
Step-by-step explanation:
The given equations are
We need isolate one of the variables, such that it appears by itself on one side of the equation.
Isolating a variable in two equations is easiest when one of them has a coefficient 1.
In equation 1, coefficient of B is 1. So, we can easily isolate one of the variables.
The equation is
Subtract 3A from both sides.
Multiply both sides by -1.
Therefore, the correct option is C.