I am a halfling monk who has recently acquired boots of striding and springing. As a halfling I have a base movement of 25 feet; however, as a monk (currently level 4) with Unarmored Movement, I have an extra 10 feet of movement, plus an extra 10 feet from the Mobile feat (PHB, p. 168) - for a total (pre-boots) of 45 feet.
The boots of striding and springing raise your walking speed to 30 feet if it is less than 30 feet.
Does this speed increase to 30 feet take effect before or after the other modifications? In other words, would my total speed be 50 feet, or remain 45 feet (as is the case without the boots)?