Given, Frequency, ν = 3 kHz = 3000 Hz

Wavelength, λ = 30 cm = 0.30 m

We know that speed, V of the wave = wavelength × frequency

V = λ ν = 0.30 m × 3000 Hz = 900 m/s

The time taken by the wave to travel a distance, d of 1.5 km is

$\mathrm{t}=\frac{\mathrm{d}}{\mathrm{V}}=\frac{1.5\times 1000 \mathrm{m}}{900 \mathrm{m}/\mathrm{s}}=\frac{15}{9} \mathrm{s}=1.67 \mathrm{s}\approx 1.7 \mathrm{s}$