Question

How did I lose 5 points?

Answer 1

x + 4 = 3x - 8, is assuming D is the midpoint, and therefore ED = DB.

all we know is that D is somewhere in EB.

$\bf E\stackrel{x+4}{\rule[0.35em]{17em}{0.25pt}}D\stackrel{3x-8}{\rule[0.35em]{10em}{0.25pt}}B \\\\\\ EB=ED+DB\implies EB=(x+4)+(3x-8)\implies EB=4x-4$