an elastic wire extended by 1.0cm where a load of 20g hangs from it. what additional load will be required to cause a further extension of 2.0cm

2 answers

yes.
clearly, k = 20g/cm
so to get an extension of 3cm, you'll need a load of 60g, or another 40g.
(yeah, I know F is weight, not mass, but that pesky g-factor cancels out)