A 6.00-kg object oscillates back and forth at the end of a spring whose spring constant is

Question:

A 6.00-kg object oscillates back and forth at the end of a spring whose spring constant is 76.0 N/m. An observer is traveling at a speed of 1.90 × 108 m/s relative to the fixed end of the spring. What does this observer measure for the period of oscillation?