As it is a straight line all the angles add up to 180 so 5s+18+48-a+8a-30= 180 so simplified 12a+36=180 then solve to get a=12.17 so then when u put 12.17 as a you get 5 * 12.17 +8 =78.85 then 48-12.17 which is clearly<78.85 then you do the final angle of 8*12.17-30 which is 67.36 so angle AOC is the biggest
