What is the smallest size of a looking glass, a person with a face 24 cm by 16 cm should purchase, which will enable him to see his whole face at a time? The distance between his eyes is 8 cm.
(a) 24 cm by 16 cm
(b) 12 cm by 8 cm
(c) 12 cm by 4 cm
(d) 6 cm by 2 cm