# How do you solve x = y + 3 and 2x + y = 9 using substitution?

Mar 14, 2016

You are given 2 variables, decide which variable you want to be substituted and what equation will be your base equation to plug in your value.

#### Explanation:

1, In this case, $2 x + y = 9$ may be use as your base equation and $x = y + 3$, since this equation does not need rearrangement to find the value of $x$, will be used to substitute (for x from your base equation) to find the value of $y$;
2. From your base equation, substitute the value of $x$;
$2 \textcolor{red}{x} + y = 9$; where $x = y + 3$ forming like this
$2 \textcolor{red}{\left(y + 3\right)} + y = 9$
3. Now, as reflected above, you have only one variable and you can now find the value $y$;
4. Then simplify the equation and combine like terms if applicable until you can arrive the value of y;
$2 \left(y + 3\right) + y = 9$
$2 y + 6 + y = 9$
$3 y + 6 = 9$
5. Isolate the term with $y$ from the numerical value by subtracting 6 both sides of the equation;
6. The value of y = 1
7. To find the value of $x$, you can use either of the equations and plug in the value of $y$;
8. Always remember to plug in values of $y$ and $x$ to check if both sides of the 2 equations are balanced.