I am unable to solve this question.  

If the area of a rhombus is 10 sq.unit . It's diagonals intersect at (0,0) if one vertex of the rhombus is (3,4) , then one of the other vertices can be ?  

I took a rhombus as ABCD . I took A as (3,4) and took O(0,0) as the point of the intersections of the diagonals . I found out OA as 5 and OB as 1 . I found out C as(-3,-4) . Now , the problem is that I am unable to find the vertex B . Please tell me how do I find out the vertex B . Thank you!