The angle of depression from the ranger at point A and the angle of elevation from the fire on the ground at Point C are congruent (interior opposite angles).
The distance from the ranger up in the tower to the fire on the ground is the hypotenuse AC of the right triangle ABC.
Coefficientis the number in front of the letter. For example, coeffient of 2b is 2. When there is no number in front of the letter the coefficient is 1.