The solution for the left side of this room
is to make the 2 bomb carts fall down at the same time.

1. Push the left bomb cart while going up.
2. Push the right bomb to left.

On the right side you need to drop the bomb on the
flame monster. So that a few blocks below the key
are being destroyed by the explosion.

Now you have to drop down the bomb
to the very bottom of the room.

Blow up this stone by dropping a bomb cart
on the head of the flame monster.