Spring and$$ Simple Harmonic Motion Problem Solving

A vertical spring scale can measure weights up to$220$ NN $.$ When $0$ N of weight $($nothing$)$ is attached to the scale, the spring is at its Natural length. When a max weight of $220$ NN $$ is attached, the spring extends by an amount of $13\mathrm{.}5$ cmcm from its Natural length.

A fish of an unknown mass hanging from the bottom of the spring oscillates vertically at a frequency of $2\mathrm{.}80$ HzHz $.$