any ideas what colors to mix together

hi everybody i was wondering if you could help me as i want to color my hair like this iv had my hair done red at toni  & guy a few months ago n have been using matrix zapppy red to keep it from lookin faded - i know that the color at the back is loreal majirouge 6.66 but im unsure of what colors to mix for the pink at the front and how much developer to use etc please any help would be great as you can probably tell im not a professional but iv heard if you get the right measurements and have confidence nothing can go wrong so thanks so much .