This problem is The Message in the Briefcase. You can solve the puzzle by answering mathematical equations, solving these equations can give you the answer to the puzzle.
So the solution is:
1. H = { -4, 5/4}
2. F = {-3/5, 1}
3. W = {-11/9, 1}
4. O = { 1/2, 2/3}
5. Z = 7 +/- SQRT217/6
6. I = 9 +/- SQRT193/-4
7. R = {-3/2. -1/3}
8. Y = -1 +/- SQRT5 / 2
9. A = 1+/- SQRT51 / 5
10. T = {1, 2/3}
11. E = -4 +/- SQRT46 / -3
12. N = {-1, 5/4}
13. C = 4 +/1 SQRT30
14. U = {-1. 10/7}
15. P = {-1, 4/3}
The answer is A RECEIPT FOR A ONEWAY TRIP TO ZURICH.