Need help figuring ABV on double fermentation

[violins]

So I made a chocolate raspberry stout a while back (turned out awesome BTW, won a 2nd place ribbon), but I can't figure out what the alcohol % is.
I started at 1.070. 10 days later it was at 1.020. I added 75 ounces of canned raspberries and that brought it back up to 1.028. 4 weeks of slow and steady fermentation later, it was down to 1.015.
So, how do I figure the ABV out? Do I figure them separately and add together? That gives me 8.253%, or is there some other formula?
Thanks in advance for the help.

 

[flylock_jac]

It's late and I'm 1/2 asleep ,but I came up with 8.4%
not sure if it's right.

 

[FlyingHorse]

Started at 1.070. Raspberries added 8 points (1.028-1.020).

Effective OG is 1.078.
FG = 1.015
ABV = (78-15) * .131 = 8.25%

Looks like you got it!