Final answer:
The domain of the profit function P = 6t + 10s includes all non-negative values for s and t, because it is practical for a business to sell zero or more units and to operate for zero or more time periods.
Step-by-step explanation:
The domain of the profit function P = 6t + 10s refers to the set of all possible values that s and t can take for which the function will have valid outputs. Since profit can be defined for all quantities (represented by t) and units sold (represented by s) that are zero or greater, the domain includes all non-negative values for s and t. This is because it is sensible for a business to sell zero or more units, and to operate for zero or more time periods, but negative values for these variables don't have a practical meaning in this context.
Therefore, the correct answer is:
B. Defined for all s ≥ 0 and t ≥ 0