Area of the parallelogram=sum of the area of the two triangles, made by any one of the diagonal, right!!!
Area of a triangle=1/2*base*height
Here, we know all the three sides- 34,20,42.
So, we have to use the Heron's formula.
Let a=34, b=20; and, c=42.
Area of a triangle, =√s(s-a)(s-b)(s-c)
=√48(48- 34)(48-20)(48-42) It is because s=48, a=34, b=20, c=42.
Therefore, are of the parallelogram= 2*336
Hope this will help you.