Assuming everything is done correctly, it should be 4× 20 = 80 points.
If 1 is wrong, subtract 4 points, subtract 1 point and subtract 5 points in * * *, that's 75 points.
1 Every mistake is actually 5 points less; He got 60 points, that is, 20 points less.
Then he got 20 ÷ 5 = 4 wrong questions and 20-4 = 16 right questions.
Checking calculation: 4× 16 = 64 points for doing the right question16, 4 points for doing the wrong question, and 64-4 = 60 points.