[tex]\\ \tt\hookrightarrow a/3=-5a[/tex]
[tex]\\ \tt\hookrightarrow a=-15a[/tex]
Only 0 can be the solution
#b
[tex]\\ \tt\hookrightarrow 12-b=12.5b[/tex]
[tex]\\ \tt\hookrightarrow 12=13.5b[/tex]
[tex]\\ \tt\hookrightarrow b=12/13.5[/tex]
[tex]\\ \tt\hookrightarrow b=0.8[/tex]
#c
[tex]\\ \tt\hookrightarrow -0.1=-10c[/tex]
[tex]\\ \tt\hookrightarrow 10c=0.1[/tex]
[tex]\\ \tt\hookrightarrow c=0.01[/tex]