Shoutout to vialia for being the best answered and for coming in clutch

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?

Could somebody me with this radical simplification?

Anyone? 15m is what percent of 60m; 3m; 30m; 1.5 km?