Answer
$= \frac{5-7x^{2}}{x^{4}}$
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 only need to multiply the second fraction by $x^{2}/x^{2}$
2) Subtract
$= \frac{5}{x^{4}} - \frac{7}{x^{2}}$
$= \frac{5}{x^{4}} - \frac{7x^{2}}{x^{4}}$
$= \frac{5-7x^{2}}{x^{4}}$
