Answer:
C.

Explanation:
We have been given a set of equations as:
Equation A:

Equation B:

We can see that the given set of equations represent system of linear equation.
We will use substitution property of equality, which states when
, then x can be substituted in any equation in place of y and y can be substituted in place of x in any equation as well.
To solve our given system of equations we need to equate our given equations as:

Therefore, option C is the correct choice.