Comment: We can consider the expression on the left hand side of the equation as a function of $x$ giving $ f(x) = 5x - 10$ . Now the problem can be restated: to find a $x$ where $f(x) = 20$. This problem and its solution can be visualized both on the graph and the mapping diagram for the function $f$.

**See also Example
LEQ.3** for a visual approach to solving a linear equation that parallels the usual algebraic steps.

For the graph of $f$: Find
$y=20$ on the Y axis , then find the point on the graph of
$f$ with second coordinate $20$, determine it's first
coordinate, $6$, and that is the desired value for $x$. |
For the mapping diagram of $f$:
Find $y=20$ on the target axis , then find $x$ on the source
axis with the function arrow pointing to $20$. |

To do this, look for the point where the line $y=20$ intersects the line that is the graph of $f$ | To do this, find the focus point of
$f$, $F= [5, -10]$ on the mapping diagram. [Use Geogebra?]
Draw the line through F and the point $y=20$, to find the
point of intersection of this line with the X axis, $x=6$,
which is the desired value for $x$. |