Answer:
The amount added to the GDP is $17000.
Step-by-step explanation:
The value added to the GDP = number of tires sold×selling price of 1 tire + number of tires unsold ×cost price of 1 tire 
 = 300 ×$50 + 100×$20
 = $15000 + $2000
 = $17000
Therefore, the amount added to the GDP is $17000.