JEE Main 2017 · 9 Apr · Shift 1, Physics question 13

A standing wave is formed by the superposition of two waves travelling in opposite directions. The transverse displacement is given by
$$y(x,t)=0.5\sin\left(\frac{5\pi}4x\right)\cos(200\pi t).$$
What is the speed of the travelling wave moving in the positive $x$ direction ?

($x$ and t are in meter and second, respectively.)