Answer:
x=15
Step-by-step explanation:
Use Pythagorean Theorem to solve for length x.
[tex]x^2=9^2+12^2[/tex]
[tex]x^2=81+144[/tex]
[tex]x^2=225[/tex]
[tex]\sqrt{x^{2}}=\sqrt{225}[/tex]
[tex]x=15[/tex]
