Answer:
15
Step-by-step explanation:
Use the Pythagorean Thereom:
[tex]r^{2}[/tex] = [tex]9^{2}[/tex]+[tex]12^{2}[/tex]
[tex]r^{2}[/tex] = 81+144
[tex]r^{2}[/tex] = 225
[tex]r[/tex]= 15
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