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$f\left(x\right)\rightarrow f\left(x\right)+b$

The graph of $f\left(x\right)$ is shown above. Type +3 after the $f\left(x\right)$ above to see what the graph of $f\left(x\right)+3$ looks like.

The graph of $f\left(x\right)+3$ is the graph of $f\left(x\right)$ by units.
Now type -4 after the $f\left(x\right)$ above and observe what the graph of $f\left(x\right)-4$ looks like.

The graph of $f\left(x\right)-4$ is the graph of $f\left(x\right)$ by units.