Answer:
Qd = 400 units 
elasticity of demand of the Accord with respect to the price of Camry = 0.5
elasticity with respect to the price of gasoline = -0.075
Explanation:
Solution: 
The annual demand function for the Honda Accord is: 
Qd = 430 – 10 PA + 10 PC – 10 PG
Where, 
PA = Price of Honda Accord
PC = Price of Honda Camry
PG = Price of Gasoline per gallon. 
Selling Price of both cars = $20,000
Fuel Cost = $3 per gallon. 
a) Elasticity of Demand of the Accord with respect to the price of Camry. 
First, we need to calculate the number of units demanded. 
Qd = 430 – 10 PA + 10 PC – 10 PG
Qd = 430 – 10 (20) + 10 (20) – 10 (3.00)
Qd = 430 - 200 + 200 - 30
Qd = 430 - 30
Qd = 400 units
Cross-price elasticity of the Accord with respect to the price of the Camry will be:  
Cross Price = (dQd/dPC) x (PC)/(Qd)
dQd/dPC = 10
PC = 20 
Qd = 400
So,
Cross Price = 10* 20/400 
Cross Price  = 0.5
b) Elasticity with respect to the price of gasoline?
Elasticity =  (dQd/dPG)*(PG/Qd)
dQd/dPG = -10
PG = 20
Qd = 400
Elasticity  = (-10)*(3/400)
Elasticity  =  -0.075