The sum of all internal angles of a triangle is 180°, therefore
[tex]a+b+c=180[/tex]
Also, we know that
[tex]b+d=180[/tex]
We have the value of d then we can find b using the second equation
[tex]\begin{gathered} b+130=180 \\ \\ b=180-130 \\ \\ b=50 \end{gathered}[/tex]
Therefore
[tex]\begin{gathered} a+50+60=180 \\ \\ a=180-50-60 \\ \\ a=180-110 \\ \\ a=70 \end{gathered}[/tex]
The value of a is 70°
