SOLUTION
Let us make a diagram of the computer screen, note that it is in the shape of a rectangle
From the diagram above, the diagonal is given as d, and that is what we want to find.
We can see that a right-triangle has been made, with sides 16, 12 and d.
To find d, we will make use of the Pythagorean theory.
According to this theory,
The hypotenuse here is the side d, applying this we have
Hence the answer is 20 inches