Common difference is -5.
Thus, this will be an arithmetic series.
Sum is given by:
[tex]a_n = \frac{n}{2}[2a_1 + (n - 1)d][/tex]
[tex]a_{16} = \frac{16}{2}[2(7) + (16 - 1)(-5)][/tex]
[tex] = 8[14 + (15)(-5)][/tex]
[tex] = 8[14 - 75][/tex]
[tex] = 8(-61)[/tex]
[tex] = -488[/tex]
