We have the following:
Being a line bisects means that it divided the angle into equal parts, as results there are two equal angles
[tex]\begin{gathered} \text{ABD}=\text{CBD} \\ \text{ABD}=3x+6 \\ \text{CBD}=7x-18 \end{gathered}[/tex]
replacing:
[tex]\begin{gathered} 3x+6=7x-18 \\ 7x-3x=6+18 \\ 4x=24 \\ x=6 \end{gathered}[/tex]
now, replacing x
[tex]\begin{gathered} \text{ABD}=3\cdot6+6=18+6=24 \\ \text{CBD}=7\cdot6-18=42-18=24 \\ \text{ABC}=24+24=48 \end{gathered}[/tex]
