FORMULA
I would start @ the bottom using a 6%+ bleach for freehanding the last 6-7" from end-mid shaft. Base a 50/50 mix of Nlv.5+6 for root to meeting stroke of bleach using a plastic board to lay section on for color application.
METHOD
Only do the bleach ends every 2" or so, vertically traveling, by 1/2" thick sections for bleaching working in a even circumference from: front hair line-back-opposite front hairline = bleach @ 6-7",.... Base = @ root & lightly carried downwards into the bleach placement(ends-mid shaft) of about 1-1.5'. Color the 2" vertical spacing's with base color only between 2.5" bleach sections(picture has some darker base in ends not solid blond)
LAST FORMULA+METHOD
Do top blond section with a bleach+3% in same method freehand, described above but 5-6" or best guess depending on layer hair length! Freehand freshly mixed base formula =3/4 6N:1/4 5N @ 3%.
The base will be close to 1 or 1/2 lv darker than pic @ first but will fade quick more true to pic color(base 6-7N) plus using more 6 in top blond hair will not darken it too much & naturally occurring depth with more lv5N in interior hair is the normal tonality pattern of hair color naturally. Overlapping the base col-the end of bleach col, makes no set lines & produces the nice fade in col transition......Charge for col correction first col & normal $$$ for up keep services.