Triangle abc is similar to triangle lmn by the aa similarity postulate. also, m∠a = 129° and m∠c = 2(m∠m). what is m∠m?

Again, this is a triangle so the sum of the angles must be 180°, so we can say:

a+b+c=180, we are told a=129, b=2c, we will let c=M°

129+2c+c=180 combine like terms on left side

129+3c=180 subtract 129 from both sides

3c=51 divide both sides by 3

c=17°

So angle M=17°