31.
The domain of a function is the set of all values that its variable can take.
To find the domain of a function, search for restrictions over its variable in its rule of correspondence. Remember that common restrictions are:
1. The denominator must be different to 0.
2. The argument of square roots cannot be negative.
For the given function:
![f(x)=4-x](https://img.qammunity.org/2023/formulas/mathematics/college/c5djslw1r226p8yy6glsa30a5gp7my2s95.png)
In this rule of correspondence, the variable x does not appear in a denominator or inside a square root. Then, there are no restrictions over the variable x and the domain is the set of all real numbers, which can be represented using interval notation as:
![(-\infty,\infty)](https://img.qammunity.org/2023/formulas/mathematics/high-school/gt1s3h5yhehl0wy6ityf0e52fgigjd4in4.png)
To sketch the graph of the function, notice that it is the equation of a line with slope -1 and y-intercept 4: