Inactive Tutor answered 10/29/18
1) In a right triangle, if A is one of the non-right angles, H is the hypotenuse and O is the side opposite A, then sine of A = O/H. Since we know H is 18 and O is between 12 and 13, sine of A ranges between 2/3 and 13/18. From there, you can figure the range of A.
2) this is similar to the previous, except in this case we know the adjacent side and the opposite side. The opposite side is the distance from the wall to the focus point or 240 inches. The adjacent side is the distance below the mounting point height to the focus point height; 84-67 or 17 inches. The appropriate trig function in this case is tangent A = opposite/adjacent = 240/17. From there, you can figure the mounting angle.