320000
It is sixty hundred forty thousand.
64, 640, 6400, 64000, 640000, 6400000, 64000000, 640000000, 6400000000 and 64000000000 are ten multiples (not multiplies!).
One kilometre is equal to 100 x 1000 = 100000 centimetres. Therefore, 6.4 kilometres is equal to 6.4 x 100000 = 640000 centimetres.
Half of half of half of one half is one sixteenth (0.0625).
This equals one and a half.