Incremental costs can be defined as:

Costs that are expected to increase regardless of the course of action chosen.
The differences between costs incurred under alternative courses of action.
Costs incurred in the past.
Costs that are irrelevant in decision making.

The correct answer is letter "B": The differences between costs incurred under alternative courses of action.

Explanation:

Incremental Cost is the added cost of one more unit of production. Also referred to as marginal cost, is the cost incurred by the company when it makes one more unit. These costs would not have existed if production had not increased.  

Incremental costs are usually lower than the average unit cost of production. Incremental costs are always comprised of variable costs. The latter is the reason why incremental costs can also be described as the result of computing the differences of the alternative paths the firm could have chosen for its production process.

if you use only 25 for your entertainment and only 200 for the groceries that you really need and take out the 50 per month for the computer then that should be enough