We will take the new equilibrium position as y= 0
and points above it are -ve and below it are positive
We will use
1) use equation
to get value of k, x here is 2inch
Here since the block is initially above the new equilibrium position so we will
have phase constant
3) Angular frequency is given by
4) A here stands for amplitude its = 3inch in your question
That's how I do it.
Incase if you use any other position as Y = 0 than add a constant "c" in SHM's equation
c will be given by the displacement of this new position from the equilibrium position.