These 2 events are dependent on each other, which means that the second event is based on what happened on Donna's first marble toss.
For starters, there are 2 blues out of 10, which means there is a 2/10 or 1/5 chance that Donna will draw a blue one.
The next time she tosses, 1 blue is left with only 9 marbles, since Donna already drew a blue one). That means there is a 1/9 chance that Donna will come out blue.
To get the combined odds, all she has to do is multiply 1/5 by 1/9, which gives her a 1/45 chance of drawing 2 blue marbles in a row.