The strain energy stored in a linear spring is
SE = (1/2)*k*x²
where
k = the spring constant
x = the extension (or compression) of the spring
Given:
k = 470 N/m
x = 17.0 cm = 0.17 m
Therefore
SE = 0.5*(470 N/m)*(0.17 m)² = 6.7915 J
Answer: 6.8 J (nearest tenth)