Try deriving the equation you get to make sure your calculation is right.
Answer:
20.8
Step-by-step explanation:
If your using delta math ..
Use a 9 instead of a ten. for example, 7/(9 x 10) = 7/90
Probably means you need to show the workings out to the questions your answering. But that's all I can give you based on what you have posted.