The path taken by George traces the 2 sides of a right angle triangle.
i.e. 6 blocks and 8 blocks.

The straight distance between him and office forms the hypotenuse of this right triangle.

Applying the Pythogaras Theorem, Hypotenuse^2 = side1^2 + side2^2

Hence the distance between George and office = 

=  = 10 blocks.

:)