Multiply the 2 binomials using FOIL:
(2x + 6)(3x - 9)
First-Outside-Inside-Last:
(a + b)(c + d) = (a * c) + (b * c) + (a * d) + (b * d)
a = 2x, b = 6, c = 3x, and d = -9
(2x + 6)(3x - 9) = (2x * 3x) + (6 * 3x) + (2x * -9) + (6 * -9)
(2x + 6)(3x - 9) = 6x2 + 18 - 18x - 54