If (0.4x+1/x) = 5, what is the value of (0.064x^3+1/(x^3))?

If x + \(\frac{1}{x}\)  = n

then, $x^3 +\frac{1}{x^3}$ = n³ - 3 × n

If $(0.4x+\frac{1}{x}) = 5$

then, $(0.064x^3+\frac{1}{x^3})$ = 5³ - 3 × 0.4 × 5

$(0.064x^3+\frac{1}{x^3})$ = 125 - 6 = 119