A Challenging Problem!

One Day , 7 friends A,B,C,D,E,F,G went to restaurant for birthday treat of their friend Albert. All 7 sit in the same way as mentioned above. Albert ordered a 420mL bottle of juice which was to be shared by all 7. Albert in order to amaze them with his mathematical skills, went to each one of them and divided the juice in the 7 glasses unequally. He then asked A to divide his share into 6 equal parts and pour it into the glasses of rest of the 6 friends. In exactly the similar way, he told B to divide his present share into 6 equal parts and pour it into the glasses of rest of the 6 friends. This went up in the same order as they are sitting, till all of them had done the same task. After all this sharing, the 7 friends still had the same amount that they had right in the beginning. Find out how much juice was served to A and C. The answer will be sum of the amounts served to A and C. (eg . If amount served to A = 12 mL and that to C = 8mL then your answer will be 12+8 = 20mL )