To find the angle A we need to find first the value of x. To do this we need to use the fact the the addition of the interior angles of any triangle is 180°.
The right side angle is equatl to 4x+4 since its vertically opposite to the one shown in the picture. The upper angle is 100° since it has to be supplementary to the angle of 80° shown in the picture.
With this in mind we have the equation:
[tex](4x+4)+(4x+4)+100=180[/tex]
Solving for x we have:
[tex]\begin{gathered} (4x+4)+(4x+4)+100=180 \\ 8x+108=180 \\ 8x=180-108 \\ 8x=72 \\ x=\frac{72}{8} \\ x=9 \end{gathered}[/tex]
Once we know the value of x we plug it in the expression for the angle A:
[tex]4(9)+4=40[/tex]
Therefore the angle A is 40°.
