This is another application of the FOIL. Multiply 4p to 4p and -1 to get 16p^2 - 4p, then multiply 1 to 4p and -1 to get 4p - 1. Add them together to get 16p^2 -1. For the future you can think of this as the same thing as 4p(4p - 1) + 1(4p - 1). Let me know if you have any questions.