I dont understand the logic..seems like such a simple problem:(
don't beat yourself up so much. Most of people happen to stumble even at the easy problems (including me). I'll give you an explanation in words. Just look at the post of gmatblackbelt while you read this. Remember to look at each two lines as a pair (first and second are together, third and fourth are together, fifth and sixth are together and so on):
first two pairs represent what is stated in the problem - a proportion
second two represent what is done when outside unknowns are matched vs. inside unknows (look above)
third two mean that if you combine P coffee from x and y mixture you will get 24 (same thing for V)
This one is the key. To solve this problem you will need to replace Vx and Vy with Px and Py(because it is what you were asked to find). You just need to look at the lines above to figure out how much is it
Next line. Because you cannot solve the equation with two unkowns you need to multiply the equation above with -5
Then, you will eliminate 5py with -5py and sum up all other number and solve the equation.
It does seem complicated in the beginning but once you adjust it is fairly easy.
let me now if you need anything else with this
Set your aims high, carpe diem