Hyperbolic Functions 
Hey everyone, I need help with questions on hyperbolic functions.
I was able to do part (a). 
I proved for $\sinh(3y)$ by doing this:
\begin{align*}
\sinh(3y) &= \sinh(2y +y)\\
&= \sinh(2y)\cosh(y) + \cosh(2y)\sinh(y)\\
&= 2\sinh(y)\cosh(y)\cosh(y) + (\cosh^2(y)+\sinh^2(y))\sinh(y)\\
&= 2\sinh(y)(1+\sinh^2(y)) + (1+\sinh^2(y) + \sinh^2(y))\sinh(y)\\
&= 2\sinh(y) + 2\sinh^3(y) + \sinh(y) +2\sinh^3(y)\\
&= 4\sinh^3(y) + 3\sinh(y).
\end{align*}
Therefore, $0 = 4\sinh^3(y) + 3\sinh(y) - \sinh(3y)$.
I have no clue what to do for part (b) and part (c) but I do see similarities between part (a) and part(b) as you can subtitute $x = \sinh(y)$.
But yeah, I'm stuck and help would be very much appreciated.

Hint 1: Set $\color{#C00000}{x=\sinh(y)}$. Since $0=4\sinh^3(y)+3\sinh(y)-\sinh(3y)$, we have
$$
4x^3+3x-\sinh(3y)=0
$$
and by hypothesis,
$$
4x^3+3x-2=0
$$
So, if $\color{#C00000}{\sinh(3y)=2}$, both equations match. Solve for $x$.
Hint 2: Set $c\,x=\sinh(y)$ for appropriate $c$.
