Answer
Substitute a variable in terms of the other two
Work Step by Step
One of the methods used to solve a system of three linear equations in three variables is the $\textbf{substitution }$ $\textbf{method}$. Let's note the variables by $x$, $y$, $z$.
First we choose one of the variables (let's say $x$) and write it in terms of the other two variables by solving one of the system's equations.
Then we substitute $x$ with this expression in terms of $y$ and $z$ in the other two equations of the system and obtain a system of two equations with two variables ($y$ and $z$).
We solve this system for $y$ and $z$.
Then we calculate $x$ by substituting the values of $y$ and $z$ in the expression of $x$.
