Angles C and D are supplementary, meaning they add up to 180 degrees. So, if we add 8u-48 to 5u+46, we get 13u-2. We set that equal to 180, so 13u-2=180. Add the two, so 13u=182. Divide the 13, so u=14. To double check, plug in 14 to both expressions. 8(14)-48 and 5(14)+46. 8(14)-48 is 64. 5(14)+46 is 116. If you add 64+116, you get 180, which proves your answer right! So u= 14