Answer:
Scale Factor is: When you divide the old shape by the new shape (explanation is here)
Explanation:
When you have 2 shapes (lets say Y is the old shape and F is the new shape) you would divide the old shape (Y) by the new shape (F)
Another example: lets say shape F is 12 cm and shape Y is 7 cm (F being the old and Y being the new shape) you would divide 12 and 7 to get the answer to that problem