Answer:
21mm
Step-by-step explanation:
The formula for solving the area of a rhombus is : 
, where x and y are two intersecting diagonals.
In this case, we are given both values, thankfully. 6 and 7 are to be replaced with x & y. Now, the rest you have to do is simple math.
The area of the rhombus is 21mm.
This is pretty simple.
If you have a sheet that tells you your identities then you should see that
Just change
to
and get
Area of parallelogram = a x h = 24 (a = length of side) (is 'a' given in your question?)if so you can find h by, h=24/aThen the area of square is = hxh
