A mass of 0.7 kg is attached to the end of a massless spring of spring constant 0.35 N/m. It is released from rest from an extended position. After 0.8 s, the speed of the mass is measured to be 1.5 m/s. What is the amplitude of oscillation?

What is the total energy (relative to the mass at rest in the unextended position) contained in this system?