Answer:
6.037
Step-by-step explanation:
[tex]d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}\\\\U (-1,4)\quad\implies\quad x_1=-1\,,\ \ y_1=4 \\\\B (8,5)\quad\implies\quad x_2=8\,,\ \ y_2=5\\\\\frac12d=\frac23\sqrt{(8+1)^2+(5-4)^2}=\frac23\sqrt{81+1}=\frac23\sqrt{82}\approx6.037[/tex]
