A ripple-tank photograph is enlarged so that all lengths appear 1.5 times their actual size. The distance across five complete wavelengths in the photograph is 30 cm. The wave frequency is 12 Hz. What is the actual wave speed?
0.48 m/s0.48\ \mathrm{m/s}0.48 m/s
0.72 m/s0.72\ \mathrm{m/s}0.72 m/s
2.40 m/s2.40\ \mathrm{m/s}2.40 m/s
1.08 m/s1.08\ \mathrm{m/s}1.08 m/s