I need help figuring out the first part of this

Achemist has 200 ml of a 10% sucrose solution. she adds x ml of a 40% sucrose solution. the percent concentration, y, of the final mixture is given by the rational function: the chemist needs the concentration of the final mixture to be 30%. how many milliliters of the 40% solution should she add to the 10% solution to get this concentration?

The sum of two numbers is 86, and their difference is 20. find the two numbers

How do you determine whether a relationship represented as as graph is linear or nonlinear