For this case we have, by definition, a function is given in the form:
![y = f (x)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/l1jrnzvmcafef6ywhq8eeek3nouil0lvi3.png)
Where x is the independent variable and y is the dependent variable.
If we have:
![x + y = 3](https://img.qammunity.org/2019/formulas/mathematics/high-school/tphncajcxmlie7ayqfe9cf05qcgl88p7v1.png)
We can rewrite it in the following way:
![y = 3-x](https://img.qammunity.org/2019/formulas/mathematics/middle-school/50dxkcny6bagtbe6vp55jrphjsn0uff2tf.png)
Comparing with the generic definition of a function, we have that
![f (x) = 3-x](https://img.qammunity.org/2019/formulas/mathematics/middle-school/7bfv0qi16qvcvx6u7q76jou4to0bhz1kuk.png)
Answer:
A relation that could be rewritten using function notation is option b.
![x+y = 3](https://img.qammunity.org/2019/formulas/mathematics/high-school/urc305e6ghr08zt15o37t809eezc5qhjzv.png)