To solve this mixed calculation, we can first convert all the fractions to have a common denominator.

3/4 = 7/14
1/4 = 3/14

Now, we can rewrite the expression:

7/14 - 2 3/14 • 7

First, let's simplify the multiplication:

2 3/14 7 = 6/14 7 = 42/14 = 3

Now we rewrite the expression:

7/14 - 3 = 4/14 = 1/3

Therefore, the answer is 1/3.