Corresponding measures have the same ratio.
.. (x -1)/4 = (2x +1)/10
.. 5(x -1) = 2(2x +1) . . . . . . multiply by 20
.. 5x -5 = 4x +2 . . . . . . . . eliminate parentheses
.. x = 7 . . . . . . . . . . . . . . . add 5 -4x
x = 7
10, 0, -10
You just have to subtract by 10
Question 1 demonstrates the Commutative Property.
The answer would be 20 degrees.
2*20
3*20
4*20
All triangles must three degrees that equals 180.