Answer
$780$ J
Work Step by Step
We know that Hooke's Law states that $F=k x$
To calculate the work done, the limits for $x$ will be from $0$ to $50$ such that:
$W=\int_0^{50} 0.624 x=0.312[ \dfrac{x^2}{2}]_0^{50}$
or, $W=0.312[ (50)^2-0] =780$ J
