If a : b : c = 3 : 4 : 7, then the ratio (a + b + c) : c is equal to

$$\eqalign{ &\,\,\,\, {\text{ }}a{\text{ }}:{\text{ }}b{\text{ }}:{\text{ }}c \cr &\,\,\,\, {\text{ }}3{\text{ }}:{\text{ }}4{\text{ }}:{\text{ }}7{\text{ }} \cr & \boxed{\,\,3x:4x:7x\,\,\,\,} \Rightarrow 14x \cr & \therefore a + b + c = 14x \cr & c = 7x \cr & \therefore \left( {a + b + c} \right):c \cr & = 14x:7x \cr & = 2:1 \cr} $$