Evaluate the series the lower limit of summation notation is 'n = 3"

Question

8
E 5n
n=3

what do you do first?

Answer 1

one way: just list the terms:

15,20,25,30,35,40

now add 'em up.

Or, recognize this an an A.P. with
a=15
d=5
and you want to sum the first 6 terms:
S6 = 6/2 (2*15+5*5) = 165