To answer this question, the easier way is to make each of the mixed fractions expressed as improper fractions
Thus, we have 6 4/9 written as 58/9 ( we shall be extending this to the other fractions too; the key is to multiply the denominator by the whole number, then add the numerator)
3 2/9 would be expressed as 29/9
and finally 8 2/9 would be expressed as 74/9
So, we can rewrite the question as follows;
-58/9 - 29/9 - 74/9
We can see all have same denominator;
Thus, we can proceed to summing all the numerators.
We have;
(-58-29-74)/9 = -161/9
We then proceed to turn this to an improper fraction too;
Kindly find the nearest multiple of 9 less than 161, then subtract the value from 161;
That would be 153 and we are left with a difference of 8
So our final mixed fraction would be -17 8/9
Hence; -6,4/9 - 3 2/9 - 8 2/9 = -17 8/9