Can you help set up these two word problems? :(

1) At a concession stand, seven hot dogs and four hamburgers cost $21.25; four hot dogs and seven hamburgers cost $22.75. Find the cost of one hot dog and the cost of one hamburger.

2)Pure acid is to be added to a 10% acid solution to obtain 45L of a 40% acid solution. What amounts of each should be used? ____L of pure acid solution and ____L of 10% acid solution.

Word problems confuse the heck out of me :/ Thanks for your help!

With word problems I find it usefull to write down what you know.

In the first case you know that:

7 hotdogs(h) + 4 hamburgers (b) = 21.25 and that 4 hotdogs + 4 hamburgers = 22.75
We can rewrite that into an equation:
1)7h + 4b = 21.25
2)4h + 7b = 22.75

Your aim here is to find out what 1 Hamburger (h) or 1 burgers(b) costs.

We can do this by subtracting one equation with the other to remove an unknown.
To remove an unknown we first have to multiple the second equation with 1.75 to get 7h.

1)7h + 4b = 21.25
2)7h + 12.25b = 39.8125
If we subtract these equations we will get ->
-8.25b = -18.5625 -> 8.25b = 18.5626 -> b = 2.25

Now that you know B, you can find out what H is by filling in b into one of the equations.
1) 7h + 4 x 2.25 = 21.25 -> 7h + 9 = 21.25 -> 7h = 12.25 -> H = 1.75.
Hotdogs costs 1.75 and Hamburgers cost 2.25.

I haven't been able to solve your second problem.