FOR BRAINLY !
Triangle angle-sum theorem 
                                             
                                          
                                          
                                        
											 
											Answer:
v = 21
Step-by-step explanation:
3v + 4v + v + 12 degrees = 180 degrees
8v + 12 = 180
8v + 12 - 12 = 180 - 12
8v = 168
8v/8 = 168/8
v = 21
Check work:
3(21) + 4(21) + 21 + 12 = 180
63 + 84 + 21 +12 = 180