Answer
$= \frac{8- 15x^{2}}{12x^{3}}$
Work Step by Step
1) Multiply a fraction with the other denominator to obtain a common denominator between the two fractions. In this case, we multiply the first fraction by $4/4$ and the second fraction by $3x^{2}/3x^{2}$ to obtain a common denominator of $12x^{3}$
2) Subtract
$= \frac{2}{3x^{3}} - \frac{5}{4x}$
$= \frac{2(4)}{12x^{3}} - \frac{5(3x^{2})}{12x^{3}}$
$= \frac{8- 15x^{2}}{12x^{3}}$
