The capacity of Karson's home library is 400 books. If he currently has 120 books, how many more books does he have to buy to make his library 90% full?
When 90% full, Karson's library holds 90/100*400 = <<90/100*400=360>>360 books.
If he has 120 books in the library now, he needs to buy 360-120 = <<360-120=240>>240 books to make his library 90% full.
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Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
You are solving math problems. Here are some examples of how to solve the task:

Melissa sells a coupe for $30,000 and an SUV for twice as much. If her commission is 2%, how much money did she make from these sales?First find the total cost of the SUV: $30,000 * 2 = $<<30000*2=60000>>60,000
Then add the cost of the coupe to find the total cost of the cars: $60,000 + $30,000 = $<<60000+30000=90000>>90,000
Multiplying that amount by Melissa's commission rate, we find her earnings are $90,000 * 2% = $<<90000*2*.01=1800>>1800
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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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Now, solve this next question in the style of the above examples:

The capacity of Karson's home library is 400 books. If he currently has 120 books, how many more books does he have to buy to make his library 90% full?

### Response:
When 90% full, Karson's library holds 90/100*400 = <<90/100*400=360>>360 books.
If he has 120 books in the library now, he needs to buy 360-120 = <<360-120=240>>240 books to make his library 90% full.
#### 240