To simplify the expression 3а + 1/7а + в/14а - в + 1/2в, we can first combine the like terms:

3а + 1/7а + в/14а - в + 1/2в = (3 + 1/7)а + в/14а - в + 1/2в
= (21/7 + 1/7)а + в/14а - в + 1/2в
= 22/7а + в/14а - в + 1/2в

Next, we can find a common denominator for the terms involving b:

22/7а + в/14а - в + 1/2в = 22/7а + 2в/28а - 28в/28 + 14а/28
= 22/7а + 2в/28а - 28б/28 + 14а/28
= 22/7а + 2в/28а - 28/28в + 14/28в
= 22/7а + 2в/28а - 1в + 1/2в

Therefore, the simplified expression is 22/7a + 2b/28a - b + 1/2b.