Hello!
To solve this exercise, we have to put the equations isolating the x variable, look:
a)
[tex]\begin{gathered} 7+2ax=13 \\ 2ax=13-7 \\ 2ax=6 \\ x=\frac{6}{2a} \\ \\ \boxed{x=\frac{3}{a}} \end{gathered}[/tex]
b)
[tex]\begin{gathered} 4=\frac{6}{a}x+5 \\ \\ 4-5=\frac{6}{a}x \\ -1=\frac{6}{a}x \\ -1a=6x \\ 6x=-1a \\ \boxed{x=-\frac{a}{6}} \end{gathered}[/tex]
c)
[tex]\begin{gathered} -ax-20=-14 \\ -ax=-14+20 \\ -ax=6 \\ \boxed{x=-\frac{6}{a}} \end{gathered}[/tex]
