Given data:
The given equation of the line is x+3y=3.
The given equation can be written as,
![\begin{gathered} x+3y=3 \\ 3y=3-x \\ y=(1)/(3)(-x+3) \\ =-(1)/(3)x+1 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/ta1jk68b7p0x5kbwwaockpha46nak82cxn.png)
The standard equation of the line is,
![y=mx+c](https://img.qammunity.org/2023/formulas/mathematics/high-school/r9wr7tk2q8cfcans6j0owflua8au85op0h.png)
Here, m is the slope.
Compare the given equation with the standard equation of the line.
m=-1/3
Thus, the slope of the line is -1/3.