When added, these two angles are supplementary, meaning that their sum is 180. This means that we can do the following to find x, and eventually DBC:
3x+67+4x+50=180
Simplifies to:
7x+117=180
Then by the Subtraction Prop. of Equality:
7x=63
Then divide by 7 on both sides to get that x=9.
We then substitute 9 into angle DBC.
4(9)+50
=36+50
DBC=86
:)