A $2-$kg block is attached to a horizonal icteal spring with a spring constant of $200\frac{N}{m}.$At its equilibrium length the block has a speed of $15\mathrm{.}4\frac{m}{s}.$ What is the maximum elongation $($allil$)$ of the spring?

a$.0\mathrm{.}8m$

b$.1\mathrm{.}2m$

c$.2\mathrm{.}3m$

d$.1\mathrm{.}5m$