Answer
1/2
Work Step by Step
To find the length of the dashed line, we subtract the two lengths next to the dashed line by the overall length. Doing this, we find:
$$ =\frac{7}{8}-\frac{3}{16} -\frac{3}{16} \\ = \frac{14}{16} - \frac{3}{16} -\frac{3}{16} \\ =\frac{8}{16} \\ =\frac{1}{2} $$
