- Wolfram|Alpha shows that your values of x are correct. I assume you can correctly calculate the double derivative of a quartic and substitute these values of x into it to determine their nature. And I assume you can correctly substitute these values into the equation for y to get the y-coordinates.
If you want answers checked you will need to post all of your work. (I help students when they're stuck, I don't check answers when the student clearly knows what to do).