"This is 9.99 yuan."
The hover-over hints on 9.99 are conspicuously missing. I think this is critically important on this exercise.
Probably depends upon the interpretation of the English. In the context that you are handing over $9.99 and you say "This is $9.99" then that would be "這是九塊..."
But in the context that you're saying for the price of something "How much is this?" "This is $9.99" then you're really saying "This costs $9.99" and that is probably where the approved answer "這個九塊..." comes from.
I'm not sure if this is accurate or not but sometimes I hear people just drop the last "feng"
Ive been in china for a year now, bever seen or heard of fen, only mao and kuai
That is correct, they are no longer used in China, though they were used historically, and of course you would use this vocabulary if you were speaking about another country’s currency using Chinese.
As of early May 1 2018, the answer tiles for this unit (and perhaps others?) are missing in the iPad version, OK on iPhone and desktop though.