The multiplier you would use to find the new value would be 0.4.
The reason for this is that 100%-60% =40%. This is the part of the value it will keep. 40% is the same as 0.4.
This decimal represents the part of the original price that is it still worth.
The multiplier is 0.4 because that it what you would multiply $80 by to find the new value.