First, we substitute the value of a into the equation:

(4 1/5 - 1 6/35) - (1 6/35 + 5/7)

Next, we simplify each term:

4 1/5 = 4 + 1/5 = 21/5
1 6/35 = 1 + 6/35 = 41/35
5/7 = 5/7

So the equation becomes:

(21/5 - 41/35) - (41/35 + 5/7)

Next, we simplify the equation further:

21/5 - 41/35 = (217)/(57) - 41/35 = 147/35 - 41/35 = 106/35
41/35 + 5/7 = (417)/(357) + 5/7 = 287/245 + 25/35 = (287 + 175)/245 = 462/245

Now, the equation is:

(106/35) - (462/245)

To subtract these fractions, we find a common denominator:

35 and 245 have a common multiple of 245, so we write both fractions with a denominator of 245:

(106 7)/(35 7) - 462/245 = 742/245 - 462/245

Next, we subtract the fractions:

742/245 - 462/245 = (742 - 462)/245 = 280/245 = 28/25

Therefore, (4 1/5 - a) - (a + 5/7) = 28/25 when a = 1 6/35.