Given matrix is

$\begin{vmatrix} s+c & a & b \\ c & s+a & b \\ c & a & s+b \end{vmatrix}$

$r1=r1-r2$

$\begin{vmatrix} s+c-c & a-(s+a) & b-b \\ c & s+a & b \\ c & a & s+b \end{vmatrix}$

$\Rightarrow \begin{vmatrix} s & -s & 0 \\ c & s+a & b \\ c & a & s+b \end{vmatrix}$

$\Rightarrow c2=c1+c2$

$\begin{vmatrix} s & 0 & 0 \\ 0 & s & -s \\ c & a+c & s+b \end{vmatrix}$

$\Rightarrow s(s(s+b)) - (-s(a+c))$

$s(ss+sb+sa+sc)$

$s(ss+ss)$

$s(2s^2)$

$2s^3$