Step-by-step explanation: As you have 180 degress in a triangle all you need to do is add 99 and 50 = 99+50=149. Then you do 180 minus 149 =180-149 = 31. Since you know the total is 180 as there is 180 degress in a triangle add 99 and 50 and 31 = 99+50+31=180
