I need guidance please

6. Is 3 and upper bound for the positive roots of 4x4 - 15x3 - 7x2 -91 - 2 =0? 7. Is - 3 a lower bound for the negative roots of 2x3 + 3x2 - 5x - 7 = 0? 8. Find all the roots of 4x4 - 813 - x2 + 8x - 3 = 0. 9. If P(x) is a polynomial with rational coefficients that has - 123, 0, 3 + i as roots, list any other numbers that also must be roots of the equation. 10. Solve the following system using Gauss-Jordan elimination. x - 2y + 3z = 11 x-y+z=2 2x - 4y + 72 = 27