The ladder forms the hypotenuse of a right triangle. The height is given by Pythagoras=√(25^2-6^2)=√(625-36)=√589=24.27 feet approx. Depending on the friction of the ladder on the ground, this height will reduce as the ladder moves away from the wall, and increase if the ladder is moved nearer the wall.
The slope is √589/6=4.045 approx. This tangent corresponds to 76.11 degrees.