Answer:
[tex]c=15[/tex]
Step-by-step explanation:
Use the Pythagorean Theorem.
[tex]a^2+b^2=c^2 \\ \\ 9^2+12^2=c^2 \\ \\ 81+144=c^2 \\ \\ c^2=225 \\ \\ c=\sqrt{225} \\ \\ c=15[/tex]