Hi Jump Boots Room
|Adjacent rooms||Hi Jump Energy Tank Room|
After collecting the item, you will want to jump into the door transition so that you can go up to collect the missile pack (unless you're only collecting 15 missiles).
After collecting the item, run off of the end of the pillar, and downback through the door transition, so you can mockball when you hit the floor in the next room. A downback is not necessary if Samus lands on the left edge of the pillar for extra running distance. You only need to hold down (to compress Samus' hitbox) if horizontal speed is sufficient.