This is not a Duo sentence, but I came across this and don't understand the number.
It means 712,900 square kilometers. I don't understand the 点 in the number and why the 万 （10,000) is at the very end. Wouldn't 712,900 be something like 七百十二万九百 because 12 is 十二？
So the answer of 712,900 given by the exercise as the correct answer is a mistake? I need to learn Chinese numbers better. Some of them seem so logical, and some of them seem confusing to me. I think I see where you get 七十一万二千九百.... 70 before 10,000+2,900 although google translate says that is 721,900!