A mass oscillating at the end of a spring

1. A 250-g object hangs from a spring and oscillates with an amplitude of 5.42 cm. The spring constant is 4.80 N/m.
a) What is the acceleration of the object when the displacement is 4.27 cm [down]?
I put:
m=0.25 kg
d=0.0542 m
k=48 N/m
x=0.0427m
Therefore:
F=kx which leads to a=kx/m
a=(48 N/m)(0.0427 m)/0.25 kg
a=8.10 m/s^2 [up]
b) What is the maximum speed of the object?
I put:
m=0.25 kg
d=0.0542 m
k=48 N/m
x=0.0427m
a=8.10 m/s^2 [up] (I think)
Not sure which equation to use...
c) At what position will the maximum speed occur?
I'd need B to know this, please help me out.
Thanks in advance!

 

i'm sorry, what is my typo?