A triangle equals 180°, and they gave us one length already, and it says the one arm of the triangle is equal to the other so we know that the third angle is going to be the same as the second angle.
180=90+(6x+3)+(6x+3) Combine like terms 180=96+12x Subtract 96 from both sides 84=12x Divide 12 by both sides 7=x
