I assume that I can use a calculator for this because 25 degrees is not really a great number to work with in trigonometry. I will also ignore the [ ] (brackets) and | | (pipes) notations.
Okay, let's do this.
(i) Consider the triangle ABT.
We know the following relation:
(ii) Consider the triangle CBT.
Same relation as above. Let x be the angle
(iii) Consider the triangle ABD (or BCD).
Use the Pythagorean theorem (I'm the one who found it, I'm such a genious) to get DB:
(iv) Consider the triangle DBT.
Just to have a little bit more confidence in our answer, and since the mast has a fixed height (12 m) you should notice that the longer the baseline is, the smaller should the angle be.
When the baseline is:
15 m (BC), the angle is
25.7 m (AB), the angle is
29.8 m (DB), the angle is
I hope these help.