Fish are hung on a spring scale to determine their mass

Fish are hung on a spring scale to determine their mass.

a) What is the force constant of the spring in such a scale if the spring stretches 8.00 cm for a 10.0 kg load?
b) What is the mass of a fish that stretches the spring 5.50 cm?
c) How far apart are the half-kilogram marks on the scale?