Waves

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 $$\left( {{{5\pi } \over 4}x} \right)\,$$ 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.)