Let the distance from the corner is x.
The length of diagonal -12 inch.
the fiure show a right angle triangle
Apply the pythagoras theorem to find the values of x
Pytahgoras theorem state as the square of the hypotenuse is equal to sum of the squre of perpendicular and the square of base of right angle triangle,
In the given figure we have,
Hypotenuse=12
Base=x
Perpendicular=x
Substutute the value in the pythagoras theorem
The corner will be at a distance of 8.5 inch.