Y'ALL PLEASE HELP 8TH GRADE MATH PLEASE

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?

Don't know how to find x given these segment lengths

What is the value of x in the following equation. -x ^3/2 = -27