Answer is 20” for the tv screen diagonal or hypotenuse
Step by step
Pythagorean theorem states
a^2 + b^2 = c^2
Solve for hypotenuse by substituting h & w for a and b and solve for c
16^2 + 12^2 = c^2
256 + 144 = c^2
400 = c^2
Take square root of both sides
20 = c
The tv screen diagonal = 20”