Find zeros, find x intercepts, all refer solve the equation for x when y is zero.
Lets factor given function to find zeros
The function seems perfect square
16x2 gives us 4x*4x
25 gives us 5*5 or -5*-5
Since we have -40 in the middle we should try -5*-5 as factors of 25
-5*4 + -5*4 = -40 that's it so out factors will be
(4x-5)(4x-5)
(4x-5)(4x-5) = 0
4x - 5 = 0
solve this equation for x
Hope that helps