Answer
The solution set is empty.
Work Step by Step
$25x^2+16<40x$, I subtract $40x$ from both sides and then factor the trinomial:
$25x^2-40x+16<0\\
(5x-4)^2<0$
The square of all real numbers is non-negative, hence for any real number, th value of $(5x-4)^2$ is never negative.
Thus, the given inequality has no solution.