Answer:
[tex]S_{n}=315[/tex]
Step-by-step explanation:
[tex]a_{1}=7\\a_{2}=9\\a_{n}=35\\[/tex]
d=9-7=2
no of terms n,
[tex]n=\frac{a_{n-a_{1}} }{d} +1[/tex]
[tex]n=\frac{{35}-{7}}{2} +1[/tex]
[tex]n=15[/tex]
sum of series,
[tex]S_{n}=\frac{n}{2} (a_{1}+a_{n})\\\\S_{n}=\frac{15}{2} (7+35})\\\\S_{n}=315[/tex]
