3x − 7 > x + 1

$3 x-7>x+1$

$\Rightarrow 3 x-x>1+7$       ( Transposing $x$ to LHS and $-7$ to RHS)

$\Rightarrow 2 x>8$

$\Rightarrow x>4$     ( Dividing both sides by 2 )

Hence, the solution set of the given inequation is $(4, \infty)$