If a cubic equation has three real roots in geometric progression with common difference 2, then the roots are a, 2a and 4a (a indicating alpha)

Further to this, if the geometric progression had a common difference of 5, would this mean that the roots are either

a, 3a, 6a

or a, 3a, 9a?

I think it might be the first one but I'm not so sure - otherwise I wouldn't have to ask Does anyone know what it might be? Thanks