Please provide the formula for me to answer
Think of it as a triangle. 20 is the height, 5 is the side. Use the Pythagorean Theorem to find the diagonal distance. 20 squared, or 400, plus 5 squared, or 25, is 425. Now square root that. It's around 20.6. However, they might just ne asking an addition question, since you can't go through solid blocks...
