Answer
$x = 1, 2 $
Work Step by Step
$(\frac{1}{4})^{x^{2} - 3x} = 16$
$(4^{-1})^{x^{2} - 3x} = 4^{2}$
$4^{-x^{2} + 3x} = 4^{2}$
$-x^{2} + 3x = 2$
$-x^{2} + 3x - 2 = 0$
$-x^{2} + 2x + x - 2 = 0$
$-x(x - 2) + 1(x-2) = 0$
$(-x + 1)(x-2) = 0$
$-x + 1 = 0$
$-x = -1$
$x = 1$
$x -2 = 0$
$x = 2$
$x = 1, 2 $