Can someone please help me!!??

Write two subtraction equations that are equivalent to 5 + 12 = 17.

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?

Simplify (4x^2 - 8xy + 2y^2) - (9x^2 - 4xy - 7y^2) a. -5x^2 + 4xy + 9y^2 b. -5x^2 - 4xy + 9y^2 c. -5x^2 + 12xy + 4y^2 d. -5x^2 - 4xy - 5y^2