I think you are missing part of the problem. If you had another equation or a value for x you could solve it.
Answer:
In khan academy, just plot the points and the answer is yes.
Step-by-step explanation:
Use the table to plot the points and you'll figure out that it's proportional- so the answer to the question below is yes. Doesn't need too much explaining.
Assuming the sum of the opposite angle would be 180. We can easily calculate for x and ultimately solve for the angle of B. We do as follows
B + D = 180
3x-12 + x = 180
4x - 12 = 180
4x = 192
x = 48 degrees
Therefore angle B would have a measurement of 132 degrees. Hope this helps.