Let us begin by labelling the sides of the triangle
We can solve for x by applying Pythagoras theorem
[tex]hypothenuse^2\text{ = opposite}^2\text{ + adjacent}^2[/tex]
Substituting the given values:
[tex]\begin{gathered} x^2\text{ = 9}^2\text{ + 12}^2 \\ x^2\text{ = 225} \\ x\text{ = }\sqrt{225} \\ x\text{ = 15} \end{gathered}[/tex]
Answer:
x = 15
