The answer is 5000 ft
His displacement is actually the hypotenuse (c) of the triangle with sides 6 blocks and 8 blocks.
According to the Pythagorean theoreme:
c² = a² + b²
c² = 6² + 8²
c² = 36 + 64
c² = 100
c = √100
c = 10 blocks
Since 1 block is 500ft long, then 10 blocks are 5000 ft long:
1 : 500ft = 10 : x
x = 10 * 500ft / 1 = 5000 ft
