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vivianrush
Algebra 2 help please
\[\sum_{k=1}^{18}7x-4\] 18 is the stopping point because it is the number of rows. You start from 1 row to 18 rows. When you start with k=1, you can substitute for x in 7x-4---> 7(1)-4=3 so that's right in the sequence 3+....
Can you do b? Moreover, have you learned the formula for partial sums?