A 395cm oscillator has a speed of 104.5cm/s when its displacement is 2.80cm and 74.5cm/s when its displacement is 6.60cm. What is the oscillator's maximum speed?
Use the fact that the total energy must be the same in both cases.
(1/2)kX^2 + (1/2) M V^2 = constant
You need another piece of information; otherwise, you have one equation in two unknowns.
When you refer to it as a 395 cm oscillator, what is it that equals 395 cm? Do you mean 395 Hz?