The distributive property works like this:
a(b+c) = ab + ac
To split apart bigger numbers, you can change 45 into 40+5. Writing this using the distributive property looks like this:
6(40+5)
Now, like we did above with a, b, and c, you can rewrite it to this:
(6 x 40) + (6 x 5)
So, your answer is B.