\(m \frac{d v}{d t} v=P\)

\(\int_{0}^{v} v d v=\frac{P^{t}}{m} \int_{0}^{t} d t\)

\(\frac{v^{2}}{2}=\frac{P t}{m} \Rightarrow v=\left(\frac{2 P t}{m}\right)^{1 / 2}\)

\(\frac{d x}{d t}=\sqrt{\frac{2 P}{m}} t^{1 / 2}\)

\(\int_{0}^{{x}} d x=\sqrt{\frac{2 P}{m}} \int_{0}^{t} t^{1 / 2} d t\)

\(x=\sqrt{\frac{2 P}{m}} \frac{t^{3 / 2}}{3 / 2}=\sqrt{\frac{2 P}{m}} \times \frac{2}{3} t^{3 / 2}\)

\(=\sqrt{\frac{2 \times 1}{2}} \times \frac{2}{3} \times 9^{3 / 2}\)

\(=\frac{2}{3} \times 27=18\)