[tex]a+b+c=126 \\ b=2a \\ c=a:2 \Rightarrow a=2c \\ \Rightarrow b=2 \cdot 2c=4c \\ 2c+4c+c=126 \\ 7c=126 \\ c= \frac{126}{7} \\ \Rightarrow \boxed{c=18} \\ a=2c=2 \cdot 18 \\ \Rightarrow \boxed{a=36} \\ b=4c=4 \cdot 18 \\ \Rightarrow \boxed{b=72}[/tex]
