Note: (HE) in front of the numbers from 10 through 99 indicates AMOUNT numbers.
Numbers vs. Amounts (slide 3)
They are just two different ways to spell numbers really, with and without the extra "ma". I have been told that using the extra "ma" is more formal. I think both spellings should be accepted for all numbers in the course now, but please let me know if you find one that is not accepted.