-3x² + 7x + 45 = (x + 6)²

-3x² + 7x + 45 = x² + 12x +36

x² + 3x² + 12x - 7x + 36 - 45 = 0

4x² + 5x - 9 = 0

D = 25 + 4 * 4 * 9 =  169

x1 = (-5 - 13)/(4 * 2) = - 18/8 = -9/4 = -2.25

x2 = (-5 + 13)/(4 * 2) = 8/8 = 1

Ответ: х1 = -2.25

           х2 = 1