To calculate how many customers the software company has, we need to consider the net gain or loss of customers each month, and how long they stay on average.
In this case, the company gains 40 new customers and loses 40 old customers every month, so their net gain/loss is zero. However, we know that each customer stays for an average of 3 years, which means that the total number of customers is the number of new customers gained each month times the average length of time they stay.
So, to calculate the total number of customers, we can multiply the number of new customers gained each month (40) by the number of months they stay on average (36, which is 3 years in months):
40 * 36 = 1440
Therefore, the software company has 1440 customers.
Hope that helps!