Find the missing angle measure of the triangle below. show your work or provide an explanation.

A triangle always adds up to 180*.
Knowing that we add up the angles 45* and 80* to get 125*
Then you do 180* - 125* to get 55*
So the angle would be 55*.

The equation for finding missing angle measures is ∠1+∠2+∠3=180° so you put 45 and 80 into the equation: 45+80+∠3=180 then you just subtract 45 and 80 from both sides to get: ∠3=55 so your answer is 55°