$y=\frac{4}{3 x^2+48 t^2+24 x t+2}$

We need to convert it into the form of $f(k x-\omega t)$

$y=\frac{4}{3\left(x^2+16 t^2+8 x\right)+2}$

$y=\frac{4}{3(x+4 t)^2+2}$

$v=\frac{\omega}{k}$

Hence $v=\frac{4}{1}=4 \,m / s$