Answer:129 is xStep-by-step explanation:Your equation would be like this x= 45 + 6=180 (180 because the sum of the angle measures in a triangle is 180 always)so once you add 45+6 =51 the equation is now x=51=180 so you subtract 51 from both sides so it equals as this x=51=180 x =-51= -51 x= 129