find the height of a residentail floor:
22-15 = 7 floors
76.4 -54 = 22.4 meters
22.4 / 7 = 3.2 meters ( each residential floor )
now find height of ground floor:
floor 8 - 1 = 7 floors
7 floors x 3.2 meters = 22.4 meters total
31.6 meters - 22.4 meters = 9.2 meters
the ground floor = 9.2 meters