Using the definition of suplementary angles we know that the angle that contains a and the 75° added together are 180°
[tex]75+(9a+6)=180[/tex]
solve the equation for a
[tex]\begin{gathered} 81+9a=180 \\ 9a=180-81 \\ 9a=99 \\ a=\frac{99}{9} \\ a=11 \end{gathered}[/tex]
