Im not looking for an answer to a test, but i dont understand the formula of a the area of a circle and semicircle can someone explain?

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?

Guys i really need or i have to stay late up night

F(x) = 1/x g(x)=x-4 can you evaluate (g*f)(0) ? why or why not?