Option 1 states that the formula 1f=1v+1u applies only to spherical mirrors. This statement is incorrect.

Option 2 states that the formula 1f=1v+1u applies only to spherical lenses. This statement is also incorrect.

Option 3 states that the formula 1f=1v+1u applies to both spherical mirrors and spherical lenses. This statement is correct.

The New Cartesian Sign Convention is a convention used in optics to determine the signs of various quantities, such as the object distance (u), image distance (v), and focal length (f), when dealing with lenses and mirrors. According to this convention, if the object distance is positive, it is on the opposite side of the lens or mirror from which the light is coming. If the image distance is positive, the image is formed on the opposite side of the lens or mirror from where the light is coming. The focal length is positive for a converging lens or mirror and negative for a diverging lens or mirror.

Therefore, option 3 correctly states that the formula 1f=1v+1u follows the New Cartesian Sign Convention for both spherical mirrors and spherical lenses.