Whats 200x3 I tried to answer it but it difficult and I knew you guys could help me?

One-third of the people from country a claim that they are from country b, and the rest admit they are from country a. one-fourth of the people from country claim that they are from country a, and the rest admit they are from country b. in a combined census of the two countries, one-half of the total claimed to be from a. what is the ratio of the populations of country a to that of country b.

Abox of chocolates costs $7. which equation relates the number of boxes sold (x) and total cost of the boxes sold (y)?

How do you use the elimination method for this question? explain, because i really want to understand!