2 black marbles:

1 white, 1 black:

1 white, 1 non-black (this means you draw either 2 white, or 1 white and 1 red; we add the events' probabilities because they are disjoint events):
The last one is the correct answer !!
D!
Say you have the number:
3,347
You can round it to the nearest thousand by figuring out whether 347 turns out to be closer to 0 or 1,000. If it's closer to 0, you round to the nearest thousand by producing the result 3,000. Since 347 is closer to 0, it would be incorrect to round the number 3,347 to the nearest thousand by producing the result 4,000.
In this case you round to the nearest thousand by producing the result 3,000.
Simplified :(5x+4y)(5x−4y)
=(5x+4y)(5x+−4y)
=(5x)(5x)+(5x)(−4y)+(4y)(5x)+(4y)(−4y)
=25x2−20xy+20xy−16y2
=25x2−16y2
hope this helps!