The average height of three kids is 56 cm and their heights are in the proportion of 7 : 8 : 9. Find the heights of all the three.

A

42 cm, 48 cm, 54 cm

B

56 cm, 64 cm, 72 cm

C

35 cm, 40 cm, 45 cm

D

49 cm, 56 cm, 63 cm