Plz help what’s the length of the side

Answer:
12
Step-by-step explanation:
Pythagoras Theorem is clearly used in this question.
To Calculate the Hypotenuse:
C = [tex]\sqrt{a^2+b^2}[/tex]
The Adjacent angle has already given as 9, so you can factor that into the question.
In Order to calculate the Opposite angle you need to use the following formula.
[tex]b = \sqrt{c^2-a^2}[/tex]
With the integers we already have for both Hypotenuse and Adjacent factored in this will be your equation:
[tex]b = \sqrt{15^2-9^2} = 12[/tex]
Therefore you answer is 12, Hope this helps, feel free to make as brainilest.