The sum of a and c is 2*85= 170.

The sum of b and c is 2*86= 172.

So twice the sum of a, b and c is162+170+172 = 504.

The sum of Party A, Party B and Party C is 504/2=252.

Because the average value of A and B is 8 1 and the sum of A and B is 162, C is 252- 162=90.

Because the average value of A and C is 85, the sum of A and C is 170.

So b is 252- 170=82.

Because the average of ethylene and propylene is 86, the sum of ethylene and propylene is 172.

So a is 252- 172=80.

To sum up: A is 80, B is 82 and C is 90.

A little wordy \ (o)/~