$\begin{vmatrix} 76 & 18 &34\\ 14 & 12 &6\\ 90 & 30 &40 \end{vmatrix}$ Apply R1 <- R1 - R3
$\begin{vmatrix} -14 & -12 &-6\\ 14 & 12 &6\\ 90 & 30 &40 \end{vmatrix}$ Apply R1 <- R1 + R2
$\begin{vmatrix} 0 & 0 &0\\ 14 & 12 &6\\ 90 & 30 &40 \end{vmatrix}$
Therefore determinant of the matrix is 0.