Let the first term be a, 4th term be [tex]a_{4}[/tex], difference between terms be d, and sum of first nine terms be [tex]S_{9}[/tex].
[tex]a_{4}[/tex] = a + 3d
32 = 11 + 3d
3d = 32 - 11
3d = 21
d = 7
[tex]S_{9}[/tex] = [tex]\frac{9}{2} (2a + (9-1)d)[/tex]
= [tex]\frac{9}{2} (22+56)[/tex]
= 9(11+28)
= 9(39)
= 325
Sum of first nine terms is 351.
