Which of the following is not a polynomial?

In the product (2 - x)(5 - 3x)(1 - 7x), the coefficient of x² is?

(2a²b + 3b²) + (5a²b + 7b²) =

(6x - 5) × (-3x) = ?

12xy × -8x² = ?

The degree of the polynomial x⁶- 2x⁶y² + 5x³y⁷+ y⁸ is