It is never meant to use Hero's formula
The logic is that 3 sides are enough for the area. we have one and only one triangle having this figure
we can find area if we know either one of the following:
2 sides included angle
2 angles and a side
or base and height
In a DS question,we aught to see if we can find it or not,not to solve it.
For those who know Hero of Alexandria, it is a plus.