A big dog B and a small dog S are pulling horizontally in opposite directions on

A big dog B and a small dog S are pulling horizontally in opposite directions on a large bone. The bone’s rightward acceleration magnitude is aaa, the big dog’s leftward force magnitude is F_BF B
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F, start subscript, B, end subscript and the small dog’s rightward force magnitude is F_SF
S
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F, start subscript, S, end subscript. The bone slides along the table with no friction.
Across the bottom is green grass. In the center there is a brown table with a large bone on top. To the left is a black outline of a large dog facing rightwards that is pulling leftwards on the bone. To the right is a black outline of a small dog facing leftwards that is pulling rightwards on the bone. The small dog stands on a grey box.
Across the bottom is green grass. In the center there is a brown table with a large bone on top. To the left is a black outline of a large dog facing rightwards that is pulling leftwards on the bone. To the right is a black outline of a small dog facing leftwards that is pulling rightwards on the bone. The small dog stands on a grey box.
Two dogs pulling on a large bone. Big dog and small dog images courtesy of pixabay.
What is the correct expression for the mass mmm of the bone?
Consider rightward as the positive direction.