def summer_rabatt(vareliste, forpris, nypris):
    rabatt = 0
    for vare in vareliste:
        varerabatt = forpris[vare] - nypris[vare]
        rabatt += varerabatt
    return rabatt

print(summer_rabatt(["laptop", "ryggsekk"], {"laptop":5000, "ryggsekk":900},
{"laptop":4000, "ryggsekk":600}))