Tension in springs (I don't know where 2 start)

[ElectroNewby]

Homework Statement

1) a spring has an elasticity constant of 225 Newtons/meter. What is its restoring for when it's compressed of 20 centimeters ?

2) with what force must we pull a spring to pull 8 centimeters if its elasticity constant is 2 Newton/cm ?

3) we suspend a weight of 4.08 kg to a spring and it pulls 8.5 cm
a) what is the elasticity constant
b) what force do you need to put to compress the spring 15 cm ?

Homework Equations

I honestly do not know beside Lnat, m1, L1, L2 and m2 I guess
Something with Hooke's law

The Attempt at a Solution

There's something missing for me to understand this problem :|

 

[Villyer]

For 1 and 2, what equation do you have that relates the spring constant and the stretch distance with force?