\[ \frac{V^2}{gR} = \frac{b}{2h} \quad \Rightarrow \quad R = \frac{V^2 \cdot 2h}{g \cdot b} \]
Substitute the values:\[ R = \frac{(5)^2 \cdot 2 \cdot 0.85}{9.81 \cdot 1.25} = \frac{42.5}{12.2625} \approx \boxed{3.47 \, {m}} \]
The equation \[ y'' + p(x)y' + q(x)y = r(x) \] is a _________ ordinary differential equation.