A piece of bone of an animal from a ruin is found to have ${}^{14}C$ activity of $12$ disintegrations per minute per gm of its carbon content. The ${}^{14}C$ activity of a living animal is $16$ disintegrations per minute per gm. Nearly, how long ago did the animal die? (Given half life of ${}^{14}C$ is $t_{\frac{1}{2}}=5760years)$