Hello!
To find how far the ship has sailed, we need to use the distance formula. The distance formula is: [tex]d = \sqrt{(x_{2}-x_{1}) ^{2}+ (y_{2}-y_{1}) ^{2} }[/tex].
Before using the formula, we need to assign the given points to [tex](x_{1}, y_{1})[/tex] and [tex](x_{2},y_{2})[/tex]. The point (1, 2) can be assigned to [tex](x_{1}, y_{1})[/tex] and (5, 5) can be assigned to [tex](x_{2},y_{2})[/tex].
With the assigned ordered pairs, we can substitute it into the formula.
[tex]d = \sqrt{(5-1) ^{2}+ (5-2) ^{2} }[/tex]
[tex]d= \sqrt{(4) ^{2}+ (3) ^{2} }[/tex]
[tex]d = \sqrt{16 + 9}[/tex]
[tex]d = \sqrt{25} = 5[/tex]
Given that each unit represents one mile, then therefore the ship has sailed 5 miles, which is choice A.