If #125 x^(-3/4) = 64#
#color(white)("XXXXX")##(5x^(-1/4))^3 = 4^3#
#color(white)("XXXXX")##5x^(-1/4) = 4#
#color(white)("XXXXX")##x^(-1/4) = 4/5#
#color(white)("XXXXX")##1/(x^(1/4)) = 4/5#
#color(white)("XXXXX")##1/x = (4/5)^4 = 256/625#
#color(white)("XXXXX")##x = 625/256 = 2.441406#