Question regarding Bleaching hair...?

I have dyed black hair and I basically want to bleach the bottom part of my hair a semi permanent hair color like a Manic Panic color. Anyways I made a purchase online through Sallys Beauty Supply and I bought Sensitive Scalp 12% Developer (40 Volume Developer), Ion Color Brilliance Powder Lightener, and blue flash power lightener. I basically need help with measurements because I have never done this before.