Step-by-step explanation:
Since, diagonal of a parallelogram bisects it in two triangles of same area.
Hence, area of parallelogram ABCD will be twice the area of triangle ABD.
[tex]area \: of \: { \parallel}^{gm} \: ABCD \\ = 2 \times A(\triangle ABD) \\ = 2 \times 40 \\ = 80 \: {m}^{2} [/tex]
