Comment
All triangles have 180o. All triangles have 3 angles. Tri means three.
Let x be the third angle.
Equation and Solution
x + 70 + 30 = 180 Add the two angles together.
x + 100 = 180 Subtract 100 from both sides.
x = 180 - 100
x = 80
Answer
The third angle is 80 degrees <<<< answer.