Answer
Water $R_e=15000$
Air $R_e=752$
Work Step by Step
For water at $30 ^{\circ}C$
$\rho=995.7{\frac{\mathrm{kg}}{{\mathrm{m}}^{3}}},\,\mu=0.798\times10^{-3}{\frac{{\mathrm{N}}_{\cdot}{\mathrm{s}}}{{\mathrm{m}}^{2}}}$
$R_{e}={\frac{\rho V D}{\mu}}={\frac{(995.7)(3)(0.004)}{0.798\times10^{-3}}}=15,000$
For Air at $30^{\circ}C$
$\rho=1.165{\frac{\mathrm{kg}}{{\mathrm{m}}^{3}}}\;\mu=1.86\times10^{-5}{\frac{\mathrm{N}\cdot s}{{\mathrm{m}}^{2}}}$
$R_{e}={\frac{\rho V D}{\mu}}={\frac{(1.165)(3)(0.004)}{1.86\times10^{-5}}}=752$
