To simplify this expression, we can expand the terms using the distributive property:

(5c-7p)(7c+5p) - (7c-5p)(5c-7p)

Expanding the first set of parentheses:
35c^2 + 25cp - 49cp - 35p^2

Expanding the second set of parentheses:
35c^2 - 49cp - 25cp + 35p^2

Now combining like terms:
35c^2 + 25cp - 49cp - 35p^2 - 35c^2 + 49cp + 25cp - 35p^2

The middle terms (25cp, -49cp, 49cp, 25cp) cancel out:
35c^2 - 35p^2 - 35c^2 + 35p^2

Finally, we are left with 0 after combining like terms. Therefore, the answer is 0.