Sidney has 4 kittens and 3 adult cats.  She has 7 cans of cat food.  Each adult cat eats 1 can of food per day.  Each kitten eats 3/4 of a can per day.  How many additional cans of food does Sidney need to buy to feed all of her animals for 7 days.
Sidney has 3 adult cats * 1 can of food = <<3*1=3>>3 cans of food per day.
Sidney's adult cats will need 3 cans * 7 days = <<3*7=21>>21 cans for the week.
Sidney has 4 kittens * 3/4 cup of food = <<4*3/4=3>>3 cans of food per day.
Sidney's kittens will need 3 cans * 7 days = <<3*7=21>>21 cans for the week.
Sidney will need to buy 21 cans + 21 cans - 7 cans = <<21+21-7=35>>35 cans.
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