Hello.
A scale factor is a term that defines the multiplicative/divisive measurement difference between the two same shapes. The way we can find our scale factor is by dividing our new measurement by the old measurement.
681 / 3 = 227
Our scale factor is 1/227, as 3 is 1/227 of 681 - and we are looking for the scale factor to find what multiplied by 681 would give us 3.
I hope this helps!