Finding amplitude of 12.5 kg mass on spring with initial conditions

[ultrapowerpie]

Simple Harmonic Motion- Spring problem

Homework Statement

A 12.5 kg mass is suspended on a 1e^5 N/m spring. The mass oscillates up and down from the equilibrium position
$$y(t)= Asin(wt+\phi)$$

Find the amplitude of the oscillating mass

Initial position- 4.9 cm
Initial velocity= +8.64 m/s
Time= 0

Homework Equations

No idea, see below

The Attempt at a Solution

Ok, I found the frequency, which is 89.44 1/s. But, I don't know how to figure out the amplitude of this thing with the information given. I've looked, and I can't find a formula to use. If someone could show me what formula I'm supposed to use, it would be greatly appreciated.

 

[ultrapowerpie]

Ok, I figured out the amplitude and the phi. But, here's the latest part of the question

Calculate the position @ t=.0149 seconds

If A=10.83 cm
w= 89.44 (1/s)
Phi= 26.895 degrees

Plugging that into the equation, I get 6.993, yet the system says it's wrong. It also says to answer in cm, but I'm not seeing any discrepencies here. >.>