LP Problem: The Big Bang explosives company produces customized blasting compounds for use

The Big Bang explosives company produces customized blasting compounds for use in the mining industry. The 4 ingredients for these explosives are agents A, B, C and D. Big Bang just received an order for 2000 lbs of explosive. Agents A and C each costs $5 per pound, agent B costs $6 per pound, and agent D costs $3 per pound. The customer's mixture must contain at least 20% agent A, at least 30% agent B, and at least 15% each for agents C and D. Additionally, the customer insists that there must be at least twice as much agent B as agent C in the mix and that the poundage of agent A must be at least 40% of what's used for agent D. At least 200 lbs of each agent should be present in the finished product. The company wants to provide the least expensive mixture which will satisfy the customer's requirements.
a)Formulate the LP model for this problem
b)What is the optimal solution?
c)How many lbs of each agent are used in the mix?
d)What is the total cost to mix the customer order?