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mysticaldogg
the measure of ABC is 21 degrees
coolstick
Since it's a straight line, the whole line adds up to 180 degrees. Next, as x+6 and 10x+9 add up to 180 (supplementary angles), we have x+10x+9+6=11x+15=180. Subtracting 15 from both sides, we get 11x=165 and by dividing both sides by 11 we get x=15