Answer
(a) increase
(b) $\Delta l=m\lambda $
Work Step by Step
(a) We now that $\Delta l=dsin\theta $
This equation shows that the path difference is directly proportional to the angle. Thus, the path difference increases when we move from a bright fringe to the next bright fringe.
(b) We know that $\Delta l=dsin\theta $
and $ dsin\theta=m\lambda $
$\implies \Delta l=m\lambda $
