Answer:
+5
Explanation:
Imagine (or draw) a right triangle with acute angles at the vertices (1, 1) and (5, 4). The horizontal leg of this triangle has length (5 - 1), or 4, and the vertical leg has length (4 - 1), or 3. Applying the Pythagorean Theorem:
(distance between these two points) = sqrt(3^2 + 4^2) = +sqrt(25) = +5