1. [tex]a+c=15 \\ => a=15-c \\ => c=15 -a[/tex]
=> [tex]n=6*(15-c)*6+5*6*c \\ n=36*(15-c)+30c \\ n=36*15-36c+30c \\ n=540-6c[/tex]
Daca c=90, n va fi egal cu 0.
2. [tex]b=12-c \\ c=12-b[/tex]
=> [tex]n=7*5*(12-c)+6*5*c \\ n=35*12-35c+30*12-30c \\ n=420+360-65c \\ n=780-65c[/tex]
Daca c=12, n va fi egal cu 0.