Consider the following balanced incomplete block design: block Treatment 1 2 3 4 5 6 7 89 A A A A A 10 11 12 THUR A A B B - - B - B C CCC C D - B - B B C C D D D D D D - Let l, m, s and n respectively denote the number of treatments, the number of treatments in each block, the number of blocks containing the same treatment, the number of blocks having the same pair of treatments. (1) What are l, m, s and n? (2) How to find n in terms of l, m, and s? Justify your answer.