Consider the Following System $$\left\{ \begin{array} { c } 7 x + y = 54 \\y = - 7 x - 18\end{array} \right.$$

Multiple Choice

Consider the following system: $$\left\{ \begin{array} { c } 7 x + y = 54 \\y = - 7 x - 18\end{array} \right.$$ Substitute $- 7 x - 18$ for y in the first equation. How many variables does the resulting equation contain?

A) 1
B) 0
C) 2
D) 4
E) none of the above