you apply the concept of vertical angles and 180-degree angle
add 43 and 74 to get 117 now subtract it by 180 you get 63 for angle 1
now since angle 1 and 2 are vertical they are both 63
now for angle 3 you add 63 plus 79 is 142 so, we subtract 142 by 180
therefore, angle 3 is 38 degrees
remember angles cannot be negative at all!