A spring has a natural length of $15\text{cm}.$ The spring is extended by $5\text{cm}$ and then released.

The length, $L,$ of the spring $t$ seconds after release is modeled by

Show that, at some time between $0.15$ and $0.16$ seconds after release, the spring returns to its natural length.

You are trying to find a root of the equation

Make sure to get $0$ on one side of the equation before using the change of sign rule.

Give the time at which the string returns to its natural length, correct to $3$ decimal places.