abc 2

A=7.........................(1)

C=5+7=12................(2)

7=1+B, or,B=6..........(3)

so,A+B+C=7=12+6=25

$\color{#3D99F6}\boxed{A=7}$ $\implies$ $\text{equation 1}$

$C=5+A=5+7=12$ $\implies$ $\color{#3D99F6}\boxed{C=12}$ $\implies$ $\text{equation 2}$

$A=1+B$ $\implies$ $B=A-1=7-1=6$ $\implies$ $\color{#3D99F6}\boxed{B=6}$ $\implies$ $\text{equation 3}$

Finally, adding the three equations, we get

$A+B+C=7+6+12=$ $\color{#D61F06}\large\boxed{25}$ $\boxed{\text{answer}}$