Answer:
15 cm
Step-by-step explanation:
Using Pythagoras Theorem ([tex]a^{2}[/tex]+[tex]b^{2}[/tex]=[tex]c^{2}[/tex])
[tex]x^{2}[/tex] = [tex]9^{2}[/tex] + [tex]12^{2}[/tex]
[tex]x^{2}[/tex] = 81 + 144
[tex]x^{2}[/tex] = 225 = [tex]\sqrt225[/tex]
[tex]x[/tex] = 15 cm
