Question 5096
use the FOIL method (First, Outter, Inner, Last):

(8x + 5/2)(8x - 5/2)
F: 8x * 8x    = 64x^2
O: 8x * -5/2  = -20x
I: 5/2* 8x    = 20x
L: 5/2 * -5/2 = -6.25

add all the products together:

64x^2 + (-20x) + 20x + (-6.25) 

cancel out any values:

64^2 - 6.25