The diagnonals of a parallelogram bisect each other ,
so
=》 BD = 3x × 2
=》BD = 6x
and there's given that
=》
[tex] BD = \dfrac{3}{5} AC[/tex]
=》
[tex]6x = \dfrac{3}{5} \times 40[/tex]
=》
[tex]x = \dfrac{24}{6} [/tex]
=》
[tex]x = 4[/tex]
so, if x = 4 , then the given quadrilateral is a parallelogram.