Roughly speaking, "estar" (está) is used when describing something that can be changed (like emotions) and ser (es) is used when describing physical attributes and places/things that can't change. If your apartment is big, it's big. Feasibly you could change it by renovating and stuff, but speaking generally, your living space will always be the size that it is.
When that happens, you should click on "report", then click on "My answer should be accepted." It won't make your answer right to them, but hopefully someone real will read it and see if there's a glitch that needs to be fixed.
That's sad. So far, I have always been able to mark that my answer should be accepted. It doesn't change it from wrong to right, but I hope it makes someone aware that changes might need to be made.
She's saying "apartamente". I listened to it slowly. Because it is an o, not an e, at the end, the speaker should enunciate more clearly. Spanish is phonetic, and easy to spell when one hears it (except for memorizing some of the accent marks), as long as the person speaking is enunciating correctly.