From Förberedande kurs i matematik 1

In order for fractions to be added together, they need first to be rewritten so that they have the same denominator, and we do this by multiplying the numerator and denominator of each fraction by the denominator of the other fraction. So,

\displaystyle \frac{7\cdot 7}{4\cdot 7}+\frac{11\cdot 4}{7\cdot 4}=\frac{49}{28}+\frac{44}{28}\,.

Now, the numerators can be added together,

\displaystyle \frac{49}{28}+\frac{44}{28}=\frac{49+44}{28}=\frac{93}{28}\,.