Solve for X
An explanation would be nice. 
                                             
                                          
                                          
                                        
											 
											All angles in a triangle add up to 180.
7x - 4 + 5x + 8 + 90 = 180
Simplify.
12x + 94 = 180
12x = 86
x = 86/12 or 43/6 (7 1/6)