Calculating the expression:

(7/5 - 6/7) * 21/38

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

(7/5 - 6/7) = (49/35 - 30/35) = 19/35

Now, multiply by 21/38:

(19/35) (21/38) = (19 21) / (35 * 38) = 399 / 1330

So, (7/5 - 6/7) * 21/38 = 399/1330.