Solution :

a) 26, 25, 24, 22, 19, 11

b) If the set C includes the stones weighted 26, 25, 24, and 23 grams, then there are two subsets with equal weights. If at least one of these stones is not chosen, then the total weight of any 4 stones from C will be less than 98. The number of nonempty subsets of C having at most 4 elements is . Therefore, there are two such subsets,  and  with equal total weights. Then the sets  and  have equal weights.