help in word problems, urgent!

the ones that i have MAJOR problems on are 2, 4, and 6. the rest i can probably do myself.

PLEASE, i do not know who to start any of these problems.

2.

An investment firm has $100,000 to invest for a client and decides to invest it int two stocks A and B. The expected annual rate of return, or interest, for stock A is 15%, but there is some risk involved, and the client does not wish to invest more than $50,000 in this stock. the annual rate of return on the more stable stock B is anticipated to be 10%. Determine how much should be invested at each rate so that the annual interest from these investments is 12,000.

3.

A chemist has 10 ml of a solution that contains a 30% concentration of acid. How many pure acid must be added in order to increase the concentration to 50%?

4.

A radiator contains 8 quarts of a mixture of water and antifreeze. If 40% of the mixture is antifreeze, how much of the mixture should be drained and replaced by pure antifreeze so that resultant mixture will contain 60% antifreeze?

5.

Two cities are connected by means of a highway. A car leaves city A at 1:00 PM and travels at a constant rate of 40 mi/h toward city B. 30 minutes later, another car leaves A and travels towards B at a constant rate of 55 m/h. At what time will be second car overtake the first car?

6.

A pharmacist is to prepare 15 ml of special eye drops for a glaucoma patient. The eye drop solution must have a 2% active ingredient, but the pharmacist only has 10% solution and 1% solution in stock. How much of each type of solution should be used to fill the prescription?

7.

It takes a boy 45 mins to deliver the newspapers on his route; however if his sister helps, it takes them only 20 minutes. How long would it take his sister to deliver the newspapers by herself?