Find the roots of the polynomial equation -x^3+5x^2 - 11x+55=0

            x³ + 5x² - 11x + 55 = 0
x²(x) + x²(5) - 11(x) - 11(5) = 0
          (x²(x + 5) - 11(x + 5) = 0
                   (x² - 11)(x + 5) = 0
x² - 11 = 0       or        x + 5 = 0
   + 11 + 11                    - 5  - 5
       x² = 11         or          x = -5
        x = ±√(11)      or      x = -5

THere are three roots in the polynomial equation.

  4725 ft²

Step-by-step explanation:

21 gallons is 3 times 7 gallons, so we expect it to cover 3 times 1575 square feet.

  3 × 1575 ft² = 4725 ft²

21 gallons will cover 4725 square feet of wall area.