If there are 240 necklaces, and 180 necklaces were sold on the website, that means it is 240 - 180. 240 - 180 = 60. This means that 60 were sold in a "high street shop."
Therefore there were
180 online sales
and 60 shop sales.
As a ratio, it is 180 online sales to 60 shop sales. Therefore, the ratio looks like this:
180:60
180:60 = 3:1
3:1 is your answer.