Rewrite the expression:

5x + (6 1/4 - 7x) - y

Combine like terms:

5x + (6.25 - 7x) - y

Remove the parentheses:

5x + 6.25 - 7x - y

Combine like terms:

(5x - 7x) + 6.25 - y

-2x + 6.25 - y

Therefore, the simplified expression is -2x + 6.25 - y.