Well, lets start with what you know. We know that 5 horse years is equal to 15 human years. If the horse is 16, 5 times 3.2 equals 16. 5 year old horse/ 15 year old human 16 year old horse/ ? human? 3.2 times 5 is 16. To find the answer, do 3.2 times 15, or 320% of 15. Three times fifteen is 45. 20% of 16 is 3.2. 45 plus 3.2 is 47.2! Did this help you?