at what rate is the depth of the pool water increasing?

Given:
Find-:
Rate is the depth of the pool water increasing
Explanation-:
The rate of change is:
[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]Choose any two points is:
[tex]\begin{gathered} (x_1,y_1)=(2,1) \\ \\ (x_2,y_2)=(4,2) \end{gathered}[/tex]So, the rate of change is:
[tex]\begin{gathered} m=\frac{y_2-y_1}{x_2-x_1} \\ \\ m=\frac{2-1}{4-2} \\ \\ m=\frac{1}{2} \end{gathered}[/tex]So, 1/2 ft per hour