In a standard television set, the screen height is 0.75 times the screen width.

if a television set measures 30 inches along the diagonal, what is the screen width?

Refer to the figure shown below.

Let x =  the screen width.
Then the screen height is 0.75x.

Because the diagonal of the screen measures 30 inches, the Pythagorean theorem requires that
x² + (0.75x)² = 30²
x² + 0.5625x² = 900
1.5625x² = 900
x² = 576
x = 24 in

 The screen width is 24 in.