When a number is doubled and 5 is subtaracted from the result, the answer is 37.what is the number?

You need to work this question backwards.
If you know the answer is 37, you need to therefore, add 5 (because it says it has been subtracted in the question)
This will give you 42. 
Because the question then says this number has been doubled - you should halve it.
This will give you 21.
To check your answer, use this number, and do as the question shows you...
21 x 2 - 5. Does this equal 37? 
Yes, then you must be correct :)