Answer:
x = 10.19803903 meters
Step-by-step explanation:
First, you need to calculate the differences in the posts height.
8 - 6 = 2
Then you can use that to draw a right triangle and solve for the distance between the tops using Pythagorean theorem.
10² + 2² = x²
100 + 4 = x² --- solve
x² = 104 --- solve
x = 10.19803903 meters --- square root both sides
