Answer:
0° < x < 83.76°
Explanation:
Assuming a pyramid with a square base, and the height of the pyramid varies from almost zero to almost infinity.
The largest value for the angle x+2 is when the height of the pyramid is almost zero.
Then the face is an isosceles triangle with base 13 and height 14.
The angle opposite the base is then
x+2 = 2*atan(6.5/7) = 2* 42.879 = 85.76°
when the height is almost infinite, the angle is almost zero.
Therefore the range of the value of x
0° < x < 83.76°