How do you add and subtract polynomials

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.

I’m still confused on how to work the percentages

In the equation sqrt(n+5)-sqrt(11-10)=1. what is the value of n