The sequence is arithmetic, since the forward difference between consecutive terms is -9.
7 - 16 = -9
-2 - 7 = -9
etc.
This means the sequence has the formula
[tex]a_n=16-9(n-1)=25-9n[/tex]
The sum of the first 30 terms is
[tex]\displaystyle\sum_{n=1}^{30}a_n=25\sum_{n=1}^{30}1-9\sum_{n=1}^{30}n[/tex]
Recall the formulas,
[tex]\displaystyle\sum_{k=1}^n1=\underbrace{1+1+\cdots+1}_{n\text{ times}}=n[/tex]
[tex]\displaystyle\sum_{k=1}^nk=1+2+3+\cdots+n=\frac{n(n+1)}2[/tex]
Then the sum we want is
[tex]\displaystyle\sum_{n=1}^{30}a_n=25\cdot30-\frac{9\cdot30\cdot31}2=\boxed{-3435}[/tex]
