$$\left. \begin{array} { l } { f ( x ) = \frac { 3 x + 4 } { 3 } } \\ { x \right.$$
Solve for x, y
$y=\frac{4}{3\left(f-1\right)}$
Steps Using Substitution
Consider the first equation. Multiply both sides of the equation by $3$.
$$3fx=3x+4$$
Subtract $3x$ from both sides.
$$3fx-3x=4$$
Combine all terms containing $x,y$.
$$\left(3f-3\right)x=4$$
Consider the second equation. Subtract $x$ from both sides.
$$y-x=0$$
To solve a pair of equations using substitution, first solve one of the equations for one of the variables. Then substitute the result for that variable in the other equation.
$$\left(3f-3\right)x=4,-x+y=0$$
Pick one of the two equations which is more simple to solve for $x$ by isolating $x$ on the left hand side of the equal sign.
$$\left(3f-3\right)x=4$$
Divide both sides by $-3+3f$.
$$x=\frac{4}{3\left(f-1\right)}$$
Substitute $\frac{4}{3\left(-1+f\right)}$ for $x$ in the other equation, $-x+y=0$.
$$-\frac{4}{3\left(f-1\right)}+y=0$$
Add $\frac{4}{3\left(-1+f\right)}$ to both sides of the equation.
