These 3 questions are about Hooke's law. The answers have already been provided in bold. So I'm looking to see the work about how to get these answers for note taking. Thanks in advance for the help.

2. An object with one end of a light horizontal spring attached to it rests on a frictionless surface. The other end of the spring is attached to a sturdy support. A force is then applied to the object which moves it 20.0 cm, stretching the spring in the process. It is found that an applied force of 50.0 N is needed to hold the mass in this position. (a) What is the spring constant of the spring? k = 250 N/m (b) How much work is needed to stretch the spring an additional 5.0 cm? 2.8 J (c) With the spring now stretched 25.0 cm, the applied force is removed. At the moment the object passes the point at which the spring is relaxed, it is moving at 2.0 m/s. What is the mass of the object? 3.9 kg