Answer:
33
Step-by-step explanation:
The two angles add up to 180 degrees because a straight line is 180 degrees
Add both equations and set equal to 180
3m + 138 + 7m +12 = 180
Algebra yeet
Simplify
10m +150 = 180
10m = 30
m = 3
Angle DBC is (7m + 12):
Substitute m = 3
7(3) + 12 = 21 + 12 = 33 degrees
