The angles in a triangle always add up to exactly 180 degrees. To see if this can be a triangle, add up the given angle measures. If the sum is not 180, then it cannot be a triangle.
140+43+7=190
A triangle CANNOT have the angles measures as 140, 43, and 7.
Hope this helps!!
5 - X - X = -1
5 - 2x = -1
-2x = -1 - 5
-2x = -6
X = 3.