#### Answer

(a) $f = 11.5~Hz$
(b) $\lambda = 1.14~m$
(c) $v = 13.1~m/s$

#### Work Step by Step

We can write the general equation for a wave traveling in the negative x-direction.
$D(x,t) = A~sin(kx+\omega t)$
(a) We can find the frequency.
$f = \frac{\omega}{2\pi}$
$f = \frac{72}{2\pi}$
$f = 11.5~Hz$
(b) We can find the wavelength.
$k = \frac{2\pi}{\lambda}$
$\lambda = \frac{2\pi}{k}$
$\lambda = \frac{2\pi~rad}{5.5~rad/m}$
$\lambda = 1.14~m$
(c) We can find the wave speed.
$v = \lambda~f$
$v = (1.14~m)(11.5~Hz)$
$v = 13.1~m/s$