Trostani and rhox faithmender

[Bman0121]

If i have a  {Trostani, Selesnya's Voice} on the board then i cast  {Rhox Faithmender} it resolves do i gain 5 life or 10 life?

[Keyeto]

You would gain 10 life. Trostani's ability triggers when a creature enters the battlefield under your control. Since the Faithmender is on the battlefield when the trigger resolves, it will double the life gained from the triggered ability from 5 life to 10.

RESOLVED

[Teysa karlov]

You would gain 10 life. Trostani's ability triggers when a creature enters the battlefield under your control. Since the Faithmender is on the battlefield when the trigger resolves, it will double the life gained from the triggered ability from 5 life to 10.

I was thinking along the same lines but was not sure enough to say,