Answer: c=8
Step-by-step explanation: All three angles in a triangle add up to 180 degrees so 9c+66+42=180. First add 66 and 42 which is 108, so now you have 9c+108=180. Then subtract 108 from both sides to get 9c=72. Finally, divide each side by 9 to isolate c and you get c=8
