The answer is [tex]\boxed{7},[/tex] where [tex]a=5[/tex] and [tex]b=2.[/tex]
Solution sketch:
Apply the Pythagorean theorem to find [tex]EC[/tex] and [tex]AE,[/tex] which you then use to find [tex]AD[/tex] and [tex]BC.[/tex] Apply Heron's formula to [tex]\triangle ABC[/tex] to find that its area is 10, and then use [tex][ABC]=\frac{(AB)(CF)}{2}[/tex] (base times height over 2) to finish by solving for [tex]CF.[/tex].
