3.78
All you need to do is plug in the numbers to your calculater, but since I'm guessing your in grade school, and they don't allow calculaters yet, you would need to understand that when two negatives multiply each other, they become positive, so you can just put
0.6
x 6.3
---------
and then just multiply as usual (ignore the decimals for now)
and then you would get 378.
Now, what you would do is because there is too decimal points in the two numbers you are multiplying, you put them into 378, making it 3.78.]
I'm sorry if it was confusing, I hope it helped!