Let's take two points from your line. where it intersects with x-axis and y-axis:
A(4; 0) and B(0;4)
Now, to find the slope of the line, we use this formula:
[tex]slope=\frac{y_{1}-y_{2}}{x_{1}-x_{2}}[/tex]
So, the solution is:
[tex]slope=\frac{0-4}{4-0}=\frac{-4}{4}=-1[/tex]
