Answer 1

dx and dy calculates the distances, obviously. It returns Math.hypot(dx, dy). This function is basically the same as:
√(dx² + dy²) (calculates the distance with the Pythagorean theorem). I'm guessing it was multiple inputs. You could count up, that dx and dy was 4 and 6 (doesn't matter if positive or negative). 4² + 6² equals 50, and you can then guess that its square root is a little bigger than seven (√49)