We know that the area of a triangle is half of that of a parallelogram if they are on the same base and between the same parallels.
In case △XCB, base is half.
∴ Area of △XCB=12×12×ar(ABC)
=14×ar(ABC)
Now, ar(AXCD)=ar(ABCD)−ar(XCB)
=ar(ABCD)−14×ar(ABCD)
=34×ar(ABCD)
⇒ ar(AXCD)=34×ar(ABCD)
⇒ 24=34×ar(ABCD)
⇒ ar(ABCD)=32cm2
We know that a diagonal divides a parallelogram into two triangles of equal area.
⇒ ar(ABC)=12×ar(ABCD)
=12×32
=16cm2