The slope formula is:
[tex]m=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}[/tex]
Your points are:
B: (b,c)
D: (a, 0)
Now you plug in the points into the equation
[tex]m=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}[/tex]
[tex]m=\frac{0-c}{a-b}[/tex]
[tex]m=\frac{-c}{a-b}[/tex]
The value that belongs in the green box is -c
