Which of the following could be classified as a deductible allowable expense?

Deductible allowable expenses are those costs that can be legitimately subtracted from gross income to determine taxable income. Business-related travel expenses fall under this category because they are necessary for the operation of the business. These expenses can include transportation, lodging, meals, and other costs incurred while traveling for business purposes. They must be ordinary, necessary, and directly related to the business to qualify as deductions.

In contrast, luxury personal expenses are not related to business operations and thus cannot be deducted. Unreported cash income cannot be classified as an allowable expense as it does not reflect an outgoing cost but rather an income that should be reported for tax purposes. Tax penalties paid from previous years typically cannot be deducted as they are considered punitive and not a legitimate business expense. Hence, business-related travel expenses are the only option among the choices provided that meets the criteria for being classified as a deductible allowable expense.