Answer:
25?
Explanation:
If I had to guess, I'd say 25. No angles are given, so it's not trigonometry, and without angles you have to use the given information.
Notice that the length of the bottom left side is 12, and the one across from it is 15. There's a ration of 15/12. The other given value is 20, and the one across from it is unknown. If they follow the same ratio, which they should, then it can be written as x/20, and being equal, the equation is 15/12=x/20. Now we can solve this by cross multiplying:
15/12=x/20
(15)(20)=(12)(x)
300=12x
300/12=x
25=x
I hope that this helps!