What is the work done by a spring force in a cyclic process?

As per the given figure,two blocks each of mass $250\,g$ are connected to a spring of spring constant $2\,N/m$. If both are given velocity $V$ in opposite directions,then the maximum elongation of the spring is:

$A$ car of mass $1000 \,kg$ having a velocity of $10 \,ms^{-1}$ collides with a horizontally mounted spring. If the spring constant is $4000 \,Nm^{-1}$, then the maximum compression of the spring is: (in $\,m$)

$A$ spring of force constant $800\, N/m$ has an extension of $5\, cm$. The work done in extending it from $5\, cm$ to $15\, cm$ is ............. $J$.

What is the spring constant? On what factors does the work done by a spring depend?

$A$ spring with spring constant $k$ is extended from $x = 0$ to $x = x_1$. The work done will be