First, let's simplify the fraction inside the parentheses:

2/7 + 5/21 = (6/21 + 5/21) = 11/21

Now, we can rewrite the expression as:

(11/21) ÷ 1 4/7

To divide by a mixed number, we first need to convert the mixed number to an improper fraction:

1 4/7 = 7/7 + 4/7 = 11/7

Now, we can perform the division:

(11/21) ÷ (11/7) = (11/21) * (7/11) = 77/231 = 1/3

Therefore, the result of the expression is 1/3.