Answer: $3,350 
Step-by-step explanation:
GDP is the addition of value of goods and service minus purchase of intermediate goods. 
 Formula to calculate value-added by each firm is shown below: 
 Value-added = Sales by Firm + Change in stock – purchase of raw material 
 
Value added by firm A = $5 × 200 + 0 – ($250 + $200) 
 = $550 
 Value added by firm B = $7 × 300 + 0 – ($150 + $100) 
 = $1,850 
 Value added by firm C = $1,000 + 0 - $50 
 = $950
Economy's GDP = Value added by firm A + Value added by firm B + Value added by firm C 
 = $550 + 1,850 + 950 
 = $3,350 
 
The value of GDP is $3,350