Answer:
a. The speed is 2.39 m/s
b. The acceleration of the block is 10.2
Explanation:
First, we have to do the energy balance where we consider two states, the first where the spring remains still and the second when it is stretched 0.400m:
Δx=
W_{ext}=20.4 Nm

To determine, the acceleration we solve the following equation for a:

Average speed = (total distance covered) / (time to cover the distance)
= (50 miles) / (1.5 hours)
= (50/1.5) miles/hours
= (33 and 1/3) mph .
We don't care about all that other "data" given earlier in the question.
We only need to know the total distance covered and the time it took
to cover the distance.
I think it is C) the resting position of the wave.
Any unit of acceleration must have the dimensions (form) of
(a unit of length) / (a unit of time)²