Chapter 9 - Section 9.2 - Arithmetic Sequences - 9.2 Assess Your Understanding - Page 654: 10

common difference = $3$ The first four terms are: $4, 7, 10, 13$

To find the first four terms, substitute $1, 2, 3, 4$ for $n$ in the given formula. $b_1 = 3(1)+1 = 3+1= 4$ $b_2= 3(2)+1 =6+1=7$ $b_3 = 3(3)+1=9+1=10$ $b_4 = 3(4)+1 = 12+1 = 13$ The terms increase by $3$ units, so the sequence is arithmetic with a common difference of $3$.