(y²-7) ² - 4(y-7) -45

To simplify the expression, let's distribute and combine like terms:

(y^2 - 7)^2 - 4(y - 7) - 45

Expanding the first term: (y^2 - 7)(y^2 - 7) = y^4 - 14y^2 + 49

Substituting this back into the expression: (y^4 - 14y^2 + 49) - 4(y - 7) - 45

Simplify further: y^4 - 14y^2 + 49 - 4y + 28 - 45

Combine like terms: y^4 - 14y^2 - 4y + 32

So, the simplified expression is y^4 - 14y^2 - 4y + 32.