Because multiplying by 0.10 is the same as dividing by 10. It is a decimal smaller than 1 its the same thing as multiplying something by a fraction because when you multiply a number by a fraction the number gets smaller.
So multiplying by 10 and multiplying by 0.10 are inverses of each other.
The ladder is forming a right triangle with the house. In this right triangle the hypotenuse is the measure of the ladder, and the distance between the house and he ladder is one of the sides of the triangle. To find the angle, , that the ladder is making with the ground, we are going to use a trig function that relates the adjacent side of our angle with the hypotenuse. That trig function is Cosine.
We can conclude that the ladder make with the ground a 62° angle.