A triangle, polygon, has 3 sides and 3 angles. Each side can be equal to other side and also be not equal to other but same the equal one. In terms of angle, the sum of all 3 angles of a triangle should be 180 degrees. So the values of the angles you give, you can only construct 1 triangle because the sum of all its angles is 180.
30 + 70 + 80 = 180
Have a nice day :D