Brain teaser - Two Ostrich Breeders

[1smartengineer]

Two ostrich breeders, Mandy and Marcia, were talking one day, and noticed
that if Mandy sold Marcia seven ostriches, Mandy would have exactly as
many ostriches as Marcia.
 
On the other hand, if Marcia sold Mandy seven ostriches, then Mandy would
have exactly twice as many ostriches as Marcia. How many ostriches did
each have?

[Heinz R.]

Marcia has 35, Mandy has 49.
Please get away from elementary school math and stick with engineering/physics or related maths.