I would say its the last answer
The answer would be point A.
Hope this helped you.
Answer:
a) 
b) 
Explanation:
Part a
For this case we can begin finding the period like this:

Then we know that the centripetal acceleration is given by:

And the velocity is given by:

If we replace this into the acceleration we got:

And we can replace the values and we got:

Part b
For this case we want to find a value of k such that:

Where a = 9.74, so then we can solve for k like this:

From the information given above,
Mass [M] = 28 g
Change in temperature = 29 - 7 = 22
Specific heat of iron = 0.449 [This value is constant]
The formula for calculating heat absorbed, Q is
Q = Mass * Specific heat of Iron * change in temperature
Q = 28 * 0.449 * 22 = 276.58 J<span />
Here, "Wavelength is same for both waves" it is the distance between two crests or two consecutive troughs, so, it is constant for both of them, you can easily figure it out.
In short, Your Answer would be "Wavelength"
Hope this helps!