The equation of a transverse wave on a string is
$$
y=(2.0 \mathrm{~mm}) \sin \left[\left(20 \mathrm{~m}^{-1}\right) x-\left(600 \mathrm{~s}^{-1}\right) t\right]
$$
The tension in the string is $15 \mathrm{~N}$. (a) What is the wave speed? (b) Find the linear density of this string in grams per meter.