Answer:
Formula:
[tex]length = \sqrt{ {(x _{1} -x_{2} )}^{2} + {(y_{1} -y_{2}) }^{2} } [/tex]
substitute:
[tex]l = \sqrt{ { \{7 - ( - 8) \}}^{2} + {(8 - 4)}^{2} } \\ \\ l = \sqrt{225 + 16} \\ l = \sqrt{241} \\ { \boxed{ \boxed{length = 15.5 \: units}}}[/tex]
