The points A and B are apart from each other vertically by 3 units, and horizontally by 5 units. You get those values by counting the squares on the grid in those directions. To find their distance we can just apply the Pythagorean Theorem.
[tex]\begin{gathered} 3^2+5^2=d^2 \\ 9+25=d^2 \\ d=\sqrt[]{34} \\ d\approx5.83 \end{gathered}[/tex]
