$2.$If y $=0\mathrm{.}02$ sin $(30$x $-400$t$)($SI units$),$ the velocity of the wave is

a$.$

$3/40$ m$/$s

b$.$

$40/3$ m$/$s

c$.$

$60$p$/400$ m$/$s

d$.$

$400/60$p m$/$s

e$.$

$400$ m$/$s