Notice that
[tex]\frac{6}{8}=\frac{2}{2}\cdot\frac{3}{4}=\frac{3}{4}[/tex]
Then, the lowest common denominator between 4 and 12 is 12.
Thus,
[tex]\begin{gathered} \frac{3}{4}=\frac{3}{3}\cdot\frac{3}{4}=\frac{9}{12} \\ \frac{1}{12} \\ \Rightarrow\frac{9}{12}+\frac{1}{12}=\frac{10}{12}=\frac{2}{2}\cdot\frac{5}{6}=\frac{5}{6} \end{gathered}[/tex]
However, if you are not allowed to simplify, notice that 8*3=24, 12*2=24; therefore, the lowest common denominator is 24, then
[tex]\begin{gathered} \frac{6}{8}=\frac{18}{24} \\ \frac{1}{12}=\frac{2}{24} \\ \Rightarrow\frac{18}{24}+\frac{2}{24}=\frac{20}{24} \\ \Rightarrow\frac{20}{24}=\frac{5}{6} \end{gathered}[/tex]
