Look at the pictures.
CL 2-109
The formula of a slope:
[tex]m=\dfrac{y_2-y_1}{x_2-x_1}[/tex]
We have
[tex](-5,\ 7)\to x_1=-5,\ y_1=7\\(10,\ 1)\to x_2=10,\ y_2=1[/tex]
Substitute:
[tex]m=\dfrac{1-7}{10-(-5)}=\dfrac{-6}{10+5}=\dfrac{-6}{15}=-\dfrac{2}{5}[/tex]
