The sum of the measures of the interior angles of a triangle add up to 180 degrees.
Since you have two angles of the triangle, add them up to equal 180 in an equation and solve for x (the third angle).
18 + 82 + x = 180
Combine like terms.
100 + x = 180
Subtract 100 from both sides.
x = 80
The third angle of the triangle is 80 degrees.