Let L0 be unstretched length::
Using Hookes law and gravity:
a) 10*9.8 = k*deltaL1 ...(1) using g = 9.8 m/s^2
14*9.8 = k*(delta1+0.025) ...(2) 2.5cm is 0.025m to keep units consistent
Subtract (1) from 2) to get 4*9.8 = 0.025k so k = 4*9.8/0.025 kg/s^2 or k = 1568 N/m
b) Using k in (1) we have 10*9.8 =1568*delta1 so delta1 = 10*9.8/1568 m or delta1 = 0.063m = 6.3cm
Since L0 + delta1 = 80cm we must have L0 = 80 - 6.3 = 73.7 cm