Simple Math-18 into 54

My Dearest Wife,

You will surely understand that I have certain needs that you, with your 54-year-old body can no longer fulfill. However, I am happy with you and I value you as a good wife. Therefore, after reading this letter, I hope that you will not wrongly interpret the fact that I will be spending the evening with my 18-year old secretary at the Comfort Inn Hotel. Please don't be perturbed, I shall be back home before midnight.

When the man came home, he found the following letter on the dining room table:

My Dearest Husband,

I received your letter and appreciate your honesty. I would, however, like to take this opportunity to remind you that you are also 54 years old. At the same time, I would like to inform you that while you are reading this, I will be at the Ritz Carleton with Michael, my tennis coach, who like your secretary is also 18. You being a successful businessman and with your excellent knowledge of math, will understand that we are in the same situation, although with one small difference: 18 goes into 54 a lot more times than 54 goes into 18. Therefore, I will not be back home until lunchtime tomorrow.