The television has 20 inch screen.
Therefore, the length of diagonal is 20 inches.
It is 12 inches high and let th ethe screen is x inches wide.
Therefore, by Pythagora's theorem,
[tex]\begin{gathered} 12^2+x^2=20^2 \\ 144+x^2=400 \\ x^2=256 \\ x=16 \end{gathered}[/tex]So, the television screen is 16 inches wide.