The slope of a line is given that passes through the points (x1,y1) and (x2,y2) is given by:
[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]In this case we know that:
After one month the account has $915, this can be represented by the point (1,915)
After nine months the account has $235, this can be represented by the point (9,235).
Plugging these two points in the expression for the slope we have:
[tex]\begin{gathered} m=\frac{235-915}{9-1} \\ m=\frac{-680}{8} \\ m=-85 \end{gathered}[/tex]Therefore, the slope is -85.
