Answer
$$
5.4 \mathrm{m} / \mathrm{s}
$$
Work Step by Step
The speed in left section of pipe is
$$
v_{2}=v_{1}\left(\frac{A_{1}}{A_{2}}\right)=v_{1}\left(\frac{d_{1}}{d_{2}}\right)^{2}=(15 \mathrm{m} / \mathrm{s})\left(\frac{3.0 \mathrm{cm}}{5.0 \mathrm{cm}}\right)^{2}=5.4 \mathrm{m} / \mathrm{s}
$$
