Answer:
A horizontal translation of 5 units to the left.
Step-by-step explanation:
Given the parent linear function:
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To shift vertically n units, we can simply add n to our function. Hence:

So, a vertical shift of 5 units up implies that n=5. So:

As given.
However, to shift a linear function horizontally, we substitute our x for (x-n), where n is the horizontal shift. So:

Where n is the horizontal shift.
For example, if we shift our parent linear function 1 unit to the right, this means that n=1. Therefore, our new function will be:

Or:

We notice that this is also a vertical shift of 1 unit downwards.
Therefore, we want a number n such that -n=5.
So, n=-5.
Therefore, it we shift our function 5 units to the left, then n=-5.
Then, our function will be:

Hence, we can achieve f(x)=x+5 from f(x)=x using a horizontal translation by translating our function 5 units to the left.