$20))$A spring has a length of $0\mathrm{.}200m$ when a $0\mathrm{.}300kg$ mass hangs from it$,$ and a length of $0\mathrm{.}750m$ when a $2\mathrm{.}20kg$ mass

hangs from it$.$

$($a$)$ What is the force constant $($in $\frac{N}{m})$ of the spring?

$\frac{N}{m}$

$($b$)$ What is the unloaded length $($in $m)$ of the spring?

$m$