Need help with Arithmetic Progression question

Question

The first term of an AP is 3 and the common difference 4. Find the sum of the first 28^th terms.

Answer 1

A1 = 3

A2 = 7

A3 = 11

A4 = A1 + 3(4) = 15

...

AN =A1 + (N-1)(4) = 3 +4N-4 = 4N-1

A28 = 4(28)-1 = 112-1 = 111

A28+A1 = 114

A27+A2 = 114

....

A15+A14 = 114

S28 = 14(114) = 1596