Question 664048
Just in case you are yet in need of the solution...
Set variables
x = chair
y = table
z = desk
...
Given
(1)  x+y=40 where y=40-x
(2)  y+z=83
(3)  x+z=77 where z=77-x
...
Solve for x
..
Substitution of equations 1 and 3 into the second equation
(40-x) + (77-x) = 83
Group like terms
40+77-83 = x + x
34 = 2x
Divide both sides by 2
x = $17 for the chair
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