I want so to solve this maths problem on my own but i have no idea how to solve it... I can solve it the long way but how can i do it quicker?

- Code: Select all
`The sum of the first two terms of an arithmetic progression is 18`

and the sum of the first four terms is 52. find the sum of the first eight terms

Can you guys help me please?

Thanks Allot

Peder