You didn’t even put the choices...
the answer is 10:20.
Hint for the future: be sure to write in the full problem. I only knew the answer because I had to do it myself, but people need more context if they are going to help you.
Answer:
WU corresponds with CD and the scale factor is 3
Step-by-step explanation:
Divide by any number except 0 means the same as multiply by its inverse.
The inverse of
is 
Therefore

Used the commutative property of multiplication: a × b = b × a
