IMO E
1) only tells you that X is not one of the big four. that'all. X may or may not be one of the 6
NOT SUFF

2) X paid 4.8 percent.
67.8-4.8=63. if there are 6 countries each paying 63/6 percent, then X is not one of them.
If there are five countries that paid 63/5 percent each, then X is one of the 6( if none of other 153 countries pay as much as X does)

NOT SUFF
combined:
If
remaining from the total paid by 6 countries=67.8-56=11.8
if 5th and 6th countries pay 5.9 percent each then X is not one of 6
if 5th country pays 11.8-4.8=7 percent and no other country pays as much as X, then X is one of the 6

sorry, i could not give you an "algebraic" solution.