PLEASE HELP ME!! Im really confused

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?

If x is 6, then 7x= a. 13 b. 42 c. 42x d. 76

Find an bif a = {3, 6, 9, 12) and b = {2, 4, 6, 8, 10).