I think that this quesion is missing some background, that is that Ms. Donaldson earned 907.10
So the 34.55 were deduced from this number, and the remaining amount was:
907.10-34.55=872.65
After this, further 28% were deduced, which means that 100-28=72% were left.
And this is:72%*872.55= 628.236 (which we round to 628.24!)