A spring that is .7m in length elongates to 1.06 m when a 20 newton force is exerted to stretch the spring. By how much more does the spring stretch when an additional 8 newtons of force is exerted on it?

Do i use the hooke's constant equation for this? if so, how would i set up the corresponding values?

find k.

20=k(1.06-.7)
then having k,
28=k(L-.7) find L, then subtract 1.08m