What are the first three terms of an arithmatic series in which, a1=9, an=105, and Sn=741?

Answer 1

741 / (9 + 105) = 6.5
... so there are 13 terms

(105 - 9) / (13 - 1) = 8
... the common difference is 8

Answer 2

741/(9+105)=6.5 (105-9)/(13-1)=8