Hi everyone, I am having trouble wrapping my head around a few word problem examples and I have been reading my book over and over and cannot even begin to get anywhere with them.

Example 1:

20 peperoni pizzas were delivered at a total cost of $181.

A sm. pizza costs $5 (contains 3oz. of pepperoni)

A med. pizza costs $9 (contains 4oz. of pepperoni)

A lrg pizza costs $12 (contains 5oz. of pepperoni)

5lbs 2 ounces of pepperoni were used in making these 20 pizzas.

How many pizzas of each size were delivered?

Example 2:

A dietician has two prepackaged mixtures of vitamin additives available for patients. Mixture 1 contains 5 grams of vitamin C and 3 grams of niacin; mixture 2 contains 6 grams of vitamin C and 5 grams of niacin. On an average day she needs 87 grams of niacin and 117 grams of vitamin C. How many packets of each mixture will she need?

Example 3:

A twin-engined aircraft can fly 1500 miles from city A to city B in 5 hours with the wind and make the return trip in 6 hours against the wind. What is the speed of the wind and the speed of the plane without any wind?