Explanation

(a) The given equation can be written as
$y = 4\ sin\ \left\lbrack \pi\left( \frac{t}{5} - \frac{x}{9} - \frac{1}{6} \right) \right\rbrack\ldots\ldots..(i)$
The standard equation can be written as
Y=a sin (ωt-kx+$\phi$)
$y = a\sin\left( \frac{2\pi}{T}t - \frac{2\pi}{\lambda}.x + \phi \right)\ldots\ldots.(ii)$
Equation Eqs. (i) and (ii), we get
Amplitude a=4cm
Frequency $f = \frac{1}{T} = 1/$10 Hz=0.1 Hz
Wavelength $\lambda = 2 \times 9$=18 cm
Velocity $v = f\lambda = 0.1 \times 18 = 1.8cms^{- 1}$