SOLUTION
This is a right-angled triangle and to solve for the unknown side we will use the Pythagoras theorem.
Given parameters:
Opposite side= 15
Adjacent side = 12
Hypotenuse side = x
Pythagoras theorem:

Substituting the given parameters into the equation above, we will have:
![\begin{gathered} x^2=15^2+12^2 \\ x^2=225+144 \\ x^2=369 \\ \sqrt[]{x^2}=\sqrt[]{369} \\ x=19.2094 \\ x=19.21(\text{to the nearest hundredth)} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/z635aofogye2sszcqjl24fi2ghqhm0snl5.png)
Final answer: x = 19.21