Answer
Common difference = $1$
The first four terms are: $5, 6, 7, 8$
Work Step by Step
To find the first four terms, substitute $1, 2, 3, 4$ for $n$ in the given formula.
$s_1 = 1+4 = 5$
$s_2=2+4 = 6$
$s_3 = 3+4 = 7$
$s_4 = 4+4 = 8$
The terms increase by $1$ unit, so the sequence is arithmetic with a common difference of $1$.
