You have a green creature card in hand with mana value equal to seven.
Selvala does not have summoning sickness.
({G} magic symbol) plus enough mana to cast the creature card in hand available.
Steps
Activate Selvala by paying ({G} magic symbol) and tapping it, adding an amount of ({G} magic symbol) equal to Selvala's power.
Cast any creature card in your hand with mana value seven by paying its mana cost.
Raggadragga's second ability triggers, untapping Selvala and giving it +7/+7 until end of turn.
Activate Temur Sabertooth by paying ({1} magic symbol) ({G} magic symbol) , returning the green creature with mana value seven from the battlefield to your hand.