After the accident, Mike can only type 65 words / minute - 20 words / minute = 45 words / minute. So, he will be able to finish typing the document in 810 words / 45 words / minute = 18 minutes.
This justifies what answer for what question? Q & A:
Mike can type 65 words per minute. Due to a minor accident, Mike cannot use his right hand for a while so that his typing speed is now 20 words less per minute. If he is supposed to type a document with 810 words, how many minutes will it take him to finish typing the document?
18