To find the inverse of the function $y = x - 3$, follow these steps:

1. Rewrite the function as $y = x - 3$.
2. Swap $x$ and $y$: $x = y - 3$
3. Solve for $y$: $y = x + 3$

So, the inverse of the function is $y = x + 3$, which is in the form $ax + b$, where $a = 1$ and $b = 3$.

Would you like a deeper explanation on any step or have questions? Here are 5 related questions:

1. How do you find the inverse of a quadratic function?
2. Can the inverse of any function always be found?
3. What happens if a function's inverse is not a function?
4. How does the domain and range change when finding the inverse of a function?
5. What are the graphical implications of a function and its inverse?

Tip: When finding inverses, always make sure the original function is one-to-one (passes the horizontal line test) to guarantee the inverse is a function.