Respuesta :
The exterior angle equals the sum of two interior opposite angles
x + 90 = 2x + 40
Sum of all interior angles = 180
x + 90 + (x - 10) = 180
Answers:
x + 90 + (x - 10) = 180
x + 90 = 2x + 40
The triangle angles add to 180, so
x+90+(x-10)=180 works, CHECK
2x = 100
x=50
The second one doesn't make much sense; it could be made to work without the 180 or with two 180s which cancel. It doesn't check at x=50 so we don't check either.
The third one 2x+80=180. That gives the right answer, x=50, but I don't see how to read it off the diagram so I'm not going to check it.
x+90=2x+40 makes sense; they're both the supplement to BCA. CHECK
The last one doesn't check for x=50 so we don't check it.