There are two methods available to such a problem that I know. One of which my teacher disagrees for it is too long: finding the time it takes to cover 19.6m and (19.6+4.9)m and the time difference.
The one he advises us to do is to find the speed of the body after falling 19.6m. Then use the formula:
and solving for t.
Hope it helped you thinking a little more about it. :)