Solving algebraic fractions , where is my mistake , guide

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 square pyramid has a volume of 441 cubic inches. what is the value of x? 1/7x is the height x is the base

What statement is true? 2x^2-9x+2=-1