equation of line is $\begin{aligned}
& y+9=m(x-4) \
& \therefore \quad A=\left(\frac{9+4 m}{m}, 0\right) \
& \quad B=(0,-9-4 m) \
& \therefore \quad O A+O B=\frac{9+4 m}{m}+9+4 m
\end{aligned}\begin{aligned} & \because \mathrm{m}>0 \ & =13+\frac{9}{\mathrm{m}}+4 \mathrm{m} \ & \because \frac{4 \mathrm{m}+\frac{9}{\mathrm{m}}}{2} \geq \sqrt{36} \Rightarrow 4 \mathrm{m}+\frac{9}{\mathrm{m}} \geq 12 \ & \therefore \mathrm{OA}+\mathrm{OB} \geq 25\end{aligned}$