Myopia is the inability of an eye in viewing long distant objects. The image in this case is formed before the retina. For every myopic eye, there exists a far point beyond which a clear image cannot be seen. The short-sightedness is corrected by using a concave lens which diverges and shifts the image to the retina.
(b) P = 1/f
f is the focal length in meters.
P = -4.5 D
f = 1/P
f = 1/4.5D
f = 0.22 m = 22 cm
(c) Negative sign of the focal length indicates that is a concave lens.