I don't see any way to tell, without more information. The middle four numbers could all be 21.5, and the first and sixth numbers could be the same amount above and below this value, so the average of the first five numbers would be something lower. But I see no way of telling, from what has been provided.

You can check this by added. Do your three numbers (the one you list, plus the one below and the one above) sum to the given value?

Plug your answer in, and see if it works.

Yes.

He answered 94 questions. Unfortunately, this is not divisible by 5. The number of mistakes, plus four times as many, is some multiple of 5. So there is an error somewhere here.

Yes.

Plug your numbers in, and see if they work.

Plug your numbers in, and see if they work.

Plug your numbers in, and see if they work.

The answer to any "solving" exercise can be checked by plugging it back into the original problem. So you can check your own answers!