I don’t get it. Can someone explain this to me?

Find the roots of the equation below. x^2 - 6 + 9 = 0

]supplementary angles are two angles that add up to . • complementary angles are two angles that add up to degrees. • adjacent angles share a and a • congruent angles have the measure. • an triangle has one angle that is greater than 90 degrees. • a triangle with angles 45°, 45°, and 90° would be a triangle

Sole the equation 6n + 9 = -3n - 21 - 6 for n