How Do I Solve This??.. Please Help. ASAP.?

Question

Can someone help me solve/explain the answer to this math problem please asap?
“Why is the formula N=100-0.25t not valid for t less than 0 (t<0) or for N less than 0 (N<0)??”

Answer 1

The only qualified domain for t and consequently N is a positive number. "t" (time) CANNOT be negative because the stopwatch always starts at "zero" and runs forward (increasing, positive numbers) until conclusion.

Answer 2

If t stands for time, then having n<0 means negative time.

Answer 3

You haven't given us all the info. What are N and t? If t is time, you can't have negative time.