The domestic demand for lettuce is given by: QD=4000-50P. The domestic supply for lettuce is given by: QS=100P-1400. The country is open to free trade and finds the world price of lettuce is $20. The government levies a $10 per unit tariff on imported lettuce. Calculate tariff revenue. (Do not include a "$" sign in your response. Include a negative sign (-) if the change is a reduction.)