CPM Homework Help : PCT Problem 4-46

Solve the system below for $x$ and $y$ .

$\left\{ \begin{array} { l } { a x + y = 7 } \\ { 3 x - y = b } \end{array} \right.$

Steps:

1. Add the two equations eliminating $y$ .
2. Solve for $x$ in terms of ' $a$ ' and ' $b$ '.
3. Solve for $y$ by substituting answer for $x$ back into one of the original equations.