Do answer this you need to multiply the amount by the decimal value of the percentage. To get the decimal of a percentage you divide the percentage by 100, so:
10 / 100 = 0.1,
Now you can multiply the weight by the decimal to find the 10% value:
64 * 0.1 = 6.4 pounds,
So 64 - 6.4 = 57.6 which is the decreased price.
The decreased amount is 57.6 pounds.
Hope this helps!