find the common difference of an arithmetic sequence if the first term is 18 and the fourth term is 54

Answer 1

a1 = 18

a4 = a1 + 3 d

54 = 18 + 3 d

Subtract 18 to both sides

36 = 3 d

36 / 3 = d

d = 12

Your arithmetic sequence:

18 , 30 , 42 , 54 ...