The displacement y of a particle in a medium can be expressed as $y = 10 ^ { - 6 } \sin ( 110 t + 20 x + \pi / 4 ) m$, where $t$ is in seconds and $x$ in meter. The speed of the wave is\\
(1) $2000 \mathrm {~m} / \mathrm { s }$\\
(2) $5 \mathrm {~m} / \mathrm { s }$\\
(3) $20 \mathrm {~m} / \mathrm { s }$\\
(4) $5 \pi \mathrm {~m} / \mathrm { s }$