Question

Find S7 for 3 + 8 + 13 + 18 +…

Answer 1

Figure out the difference between each term.
Each term is increasing by 5, so your equation has to have 5n in it.
Then to get the first term of 3, you have to subtract 2 from 5n.
So the equation is: 5n - 2

now just plug in 7 in place of n.

Answer 2

if you're finding the sum, then add the terms up.