Good evening, I would like a detailed step by step of this math problem:

You are a nurse practitioner at a local clinic and one of your patients is decient in calcium, iron and vitamin A. You advise him to buy two types of pills that will help. Each type of Pill I contains 4 units of calcium, 3 units of iron, 4 units of vitamin A, and costs $0.10. Each type of Pill II contains 1 unit of calcium, 2 units of iron, 7 units of vitamin A, and costs $0.15. Your patient needs a minimum of 200 units of calcium, a minimum of 250 units of iron and a minimum of 420 units of vitamin A. He wishes to minimize the cost of the pills.

Thanks in advance!