To find the resultant displacement when the pirate walks 39 meters east and 80 meters north, we can treat this as a right triangle, with the displacement being the hypotenuse. The Pythagorean theorem is used to calculate the magnitude of the displacement:

$\text{Resultant displacement} = \sqrt{(39^2 + 80^2)}$

$= \sqrt{(1521 + 6400)}$

$= \sqrt{7921}$

$= 89 \, \text{meters}$

So, the magnitude of his resultant displacement is 89 meters. The correct answer is A. 89 m.

Would you like more details or further clarification?

Here are 5 related questions to consider:

1. How would the resultant displacement change if the distances east and north were doubled?
2. What is the formula for calculating displacement in a 3D space?
3. How can you determine the direction of the displacement?
4. How would you solve this problem if the pirate had walked diagonally?
5. What is the difference between displacement and distance?

Tip: When solving problems involving displacement in two dimensions, always think about the Pythagorean theorem for calculating the shortest path.