How do i answer 15 and 16? , i have a test tomorrow

Aspring has a natural length of 8 m. if a 12-n force is required to keep it stretched to a length of 10 m, how much work w is required to stretch it from 8 m to 16 m? (round your answer to two decimal places.)

In a star, nuclear fusion occurs in the a. photosphere. b. corona. c. radiative zone. d. core.

What is the period of a wave traveling 5 m/s if its wavelength is 20 m/s