Question Difficulty

A $950$ kg car strikes a huge spring at a speed of $\backslash (21\backslash$mathrm$\{$~m$\}/\backslash$mathrm$\{$s$\}\backslash ),$ compressing it $7\mathrm{.}0$ m $.$

$($a$)$ What is the spring constant of the spring?

$\backslash [$

$\backslash$mathrm$\{$N$\}/\backslash$mathrm$\{$m$\}$

$\backslash ]$

$($b$)$ How long does the spring take to stop the car?