Answer: Let's represent the price of a plastic table as x.
Then the price of a wooden table is x + 7, and the price of a glass table is 2(x + 7) = 2x + 14.
We know that the price of a glass table is three times the amount of a plastic table, so we can set up the equation:
2x + 14 = 3x
Subtracting 2x from both sides, we get:
14 = x
So the price of a plastic table is $14. Therefore, the price of a wooden table is x + 7 = 21, and the price of a glass table is 2x + 14 = $30.
Therefore, the price of a glass table is $30.