Since BD is the bisector, the angles created are same.
Angle ABD = Angle CBD
Also,
Angle ABD + Angle CBD = Angle ABC
Given Angle ABD = 3x
Also Angle ABC = 42
Looking at the equations, we can write:
Angle ABD + Angle CBD = Angle ABC
3x + 3x = 42
Now, we solve for x using algebra:
[tex]\begin{gathered} 3x+3x=42 \\ 6x=42 \\ x=\frac{42}{6} \\ x=7 \end{gathered}[/tex]