To determine the appropriate domain for the problem, we need to consider the context of the equation provided. The equation \( n(t) = 50(1.2)^t \) calculates the number of bacteria \( n \) after \( t \) hours.
Given that the scientist is checking the population after 4 hours, the variable \( t \) represents time in hours and should be non-negative. Thus, the reasonable range for \( t \) would be between \( 0 \) and \( 4 \) hours, which corresponds to the time the bacteria are being observed.
Therefore, the appropriate domain for the problem, given the context, would be:
Option #3: \( 0 \leq t \leq 4 \)
It indicates the range of time over which the observation is made. Options #1, #2, and #4 do not correctly reflect the appropriate domain for the variable \( t \) in the context of checking the population after 4 hours.