Hello, nerdzor!

This should get you started . . .

1. Find the arithmetic progression where:

. .

We have: .

Subtract [1] from [2]: .

Substitute into [1]: .

The progression is: .

Consecutive terms will have a common difference.4. Find the value of so that:

are successive terms of an arithmetic progression.

Hence: .

. . And solve for

[The terms are: . .]