Answer:
x = 16 inches
Explanation:
Let the length of a rectangular screen is x inches.
Then from the statement of the question width of the screen will be (x -4) inches.
Now we apply Pythagoras theorem
x²+(x - 4)² = 20²
x² + x² + 16 - 8x = 400
2x²- 8x + 16 - 400 = 0
2x² - 8x - 384 = 0
x² - 4x - 192 = 0
From quadratic formula

Since length of screen can not be in negative notation.
Therefore x = 16 inches is the answer.