Answer
$\frac{13b-4a}{ab}$.
Work Step by Step
In order to add or subtract fractions, we start by making a common denominator (bottom of the fraction). Thus, we multiply 13/a by b/b and 4/b by a/a to obtain:
$\frac{13b}{ab}$-($\frac{4a}{ab}$)=$\frac{13b-4a}{ab}$.
