What you want to do is multiply one of the equations so that when the two equations are added together, one of the variables can be cancelled out and you solve for the other variable.

You can accomplish this by multiplying both sides of the bottom equation by -4

2c + 12t = $83

-20c - 12t = -$128

-18c = -$128

c = $7.11 which is the cost each chair

Substitute that value in for c in one of the equations and solve for t