Answer
$y_1$, $y_4$, $y_2$, $y_3$
Work Step by Step
A wave function is defined as $y(x,t)=Acos(kx+\omega t)$. $\omega=kv$ , so $v=\frac{\omega}{k}$. Finding $v$ values for all waves give $$v_1=\frac{3rad/s}{1rad/m}=3m/s$$ $$v_2=\frac{1rad/s}{2rad/m}=\frac{1}{2} m/s$$ $$v_3=\frac{1rad/s}{4rad/m}=\frac{1}{4}m/s$$ $$v_4=\frac{2rad/s}{1rad/m}=2m/s$$ Ordering these from greatest to least in terms of wave speed gives $y_1$, $y_4$, $y_2$, $y_3$.
