Answer:
x = 16cm
Step-by-step explanation:
[tex]C^{2}[/tex] - [tex]A^{2}[/tex] = [tex]B^{2}[/tex]
[tex]20^{2}[/tex] - [tex]12^{2}[/tex] = 256
[tex]\sqrt{256}[/tex] = 16
