(8x^2 - 9) (2x + 4)
Multiply each term in the first set of parenthesees by each term in the second set of parenthesees and add the products together. It's "first times first plus first times second plus second times first plus second times second"
(a + b)(c + d) = ac + ad + bc + bd
(8x2 + -9)(2x + 4) = . . .?
Do you see what to do next? If you still don't understand please say so