Answer:
approximately 6.708 feet
Step-by-step explanation:
We use the Pythagorean theorem to solve the problem, using 3 feet and 6 feet as the legs of a right angle triangle. The diagonal of the screen is therefore the "hypotenuse" of this right angle triangle, and can be determined via the formula:

which is approximately 6.708 feet
Z=Xk228=12kk=228/12k=19Z=18*19Z=342 57=3k57/3=k19=k again Z=8*19Z=152
hope i could help :)