Can someone please help me with all the questions?

Answer:
Here you go. It was much simpler than it looked.
Explanation:
[tex]Start\\ a^{2}+b^{2}=c^{2}\\ 9^{2}+12^{2}=c^{2}\\ 81+144=c^{2} \\ 225 = c^{2} \\ \sqrt{225} = \sqrt{c}^{2}\\ 15 = c\\ c = 15[/tex]
Consider Brainliest! Hope I helped!