0.5% means 'when the number is 100 your answer will be 0.5'.
If other words for every 100 we have, we have 0.5, therefore we must find how many 100s are in 64, because that will tell us how many 0.5s there are.
So we divide by 100, that gives us 0.64, this is how many 100s there are in 64, and so we know there is that many 0.5s.
So if our answer is 0.64 0.5s then we just multiply them 0.64*0.5 = 0.32.
0.32 is your answer.