Because u take the equation and plug in each of the values getting you G+B=666 and then you know that the Garden Table is less than the bench so u plug that in to get B-84+B=666 and then you combine like terms and get 2b-84=666 then you can solve the equations by first adding to even the equation 2b=750 then dividing 2 by 750 to get b=375.