Final answer:
The subject of this question is Mathematics and it relates to a situation involving a stationary dial and the concept of excess time used by a cell phone customer.
Step-by-step explanation:
The subject of this question is Mathematics. The question is asking about a situation where a dial remains stationary for more than 40 seconds and the variable 'X' represents the excess time used by an individual cell phone customer who exceeds their contracted time allowance.
In this case, 'X' represents the additional time used by the customer above their contracted time allowance. So, if the dial remains stationary for more than 40 seconds, the value of 'X' would be 10 because the customer is using excess time above the 40 seconds.