Question

Solve by substitution x = y - 3 2x + y = 12 Help!!

Answer 1

$x = y - 3$ 
                                             $\text{substitution}$
$2x + y = 12$ 

Start with the original equation  

$2x+y=12$ 

$2(y-3)+y=12$ 

$3y-6=12$ 

Solve for y in $3y-6=12$  

$3y-6=12$ 

$3y=12+6$ 

$3y=18$ 

$y= \dfrac{18}{3}$ 

$y=6$ 

Substitute $y=6$ into $x=y-3$

$x=y-3$
 
$x=6-3$ 

$x= 3$  

Therefore, $y=6$ and $x= 3$. 

Answer 2

Let's plug in what x =, y-3 into 2x+y=12
2 (y-3)+y=12
distribute 2 to both y and -3
2y-6+y=12
add all ys
3y-6=12
+6 both sides
3y=18
÷3 both sides

y=6

plug in y into x=y-3 to find x
x=6-3
x=3