A brick of mass 2 kg hangs from the end of a spring. When the brick is at rest, the spring is stretched by 7 cm. The spring is then stretched an additional 2 cm and released. Assume there is no air resistance. Note that the acceleration due to gravity, $g$, is $g = 980$ cm/s${}^2$.

Set up a differential equation with initial conditions describing the motion and solve it for the displacement $s(t)$ of the mass from its equilibrium position (with the spring stretched 7 cm).

$s(t) =$ cm
(Note that your answer should measure t in seconds and s in centimeters.)