Answer:
The chemist needs to add 400mL of 40% solution.
Step-by-step explanation:
The equation

gives the percent concentration
of the final mixture, when
mL of the 40% solution are added.
Now we are asked, how many milliliters
of the 40% solution should the chemist add to get final percent concentration
; this is just a matter of solving the equation

and we solve it the following way:

Thus, the chemist needs 400mL of 40% solution to get 30% concentration of the final mixture.
By using pythagorian theorem
https://youtu.be/WsjIu4XnOYA
Answer: Option C. Ellipse
Step-by-step explanation:
The general equation of an ellipse has the following form:

Where the point (h, k) is the center of the ellipse
In this case we have the equation

Note that its shape matches that of a ellipse with center (9, -2)

Therefore the answer is the obtion C