This problem can be easily solved using an overlapping sets table. Unfortunately they are very hard to depict by typing and we're not allowed to post pictures. Fortunately this problem can be solved in a different way as well.

If 7,100 titles are distributed by L and 5,200 are distributed by M, but the grand total is 9,300, we should figure out the overlap. Adding 7,100 and 5,200 gets us a total of 12,300, which is exactly 3,000 more than the total we've been told. Therefore there must be an overlap of 3,000 titles.

A. If half the titles distributed by L totals 3,550, but the overlap is 3,000, then A is not true.

B. If half the titles distributed by M totals 2,600, and the overlap is 3,000, then B is true.

C. This is obviously not true since we've proven that 3,000 titles are sold by both.
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Us this diagram to solve the answer

x=overlapping events
So, (7100-x)+(5100-x)+x=9300
x=3000
Now, logic says that B only holds .