Using Apple's 2016 10-K What was Apple's accounts receivable turnover (rounded to two decimal places) in 2015 and 2016? (Accounts receivable were $17,460,000,000 at the end of 2014.)

I'm not sure if I did it right.

Accounts Receivable turnover ratio: = Net Sales/Average Accounts Receivable.

2015

($17460 million + $16,849 million)/2 =$17154.5 million

Net Sales: $233,715 million/$17,154.5=13.62

My Answer: 2015 - 13.62 times.

2016

($16,849 million +$15,754 million)/2 = 16,301.5

Net sales: $215,639/16,301.5 = 13.22

My answer for 2016: 13.22

Please help and explain how to solve this.