Duration Increment + Spell Casting Reinforcement

[Goatface]

I did a search and didn't see it, but how are the numbers applied

say you have
Spell Casting Reinforcement 3 +30%
Spell Casting Reinforcement Mastery +20%
Duration Increment V +25%

is it added all together for a 75% bonus
or
buff x 30% x 20% x 25%
or
buff x 50% x 25%
or
another way?