Answer
$= \frac{13}{12x^{2}}$
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 $3/3$ and the second fraction by $4/4$ to obtain a common denominator of $12x^{2}$
2) Add the fractions
$= \frac{-5}{4x^{2}} + \frac{7}{3x^{2}}$
$= \frac{-5(3)}{12x^{2}} + \frac{7(4)}{12x^{2}}$
$= \frac{-15 + 28}{12x^{2}}$
$= \frac{13}{12x^{2}}$
