Your question is asking what choice the employer would make, giving the different wages of two different racial groups.
The reason why answer choice "D" would be the correct answer is because the employer would want to save money. For an employer, they need to pay the workers that work for them, but employers like to save some money to. They like to save money so they have extra money for the company. That's why the employer would think the wage for the Hispanic worker is high.
In this case, the wage for an African American would be $15. That price is lower than the Hispanic's wage, so the employer would most likely choose the African-American to work for them because they can save $3 an hour.
The only way the employer would consider hiring the Hispanic worker is if the Hispanic worker's wage matches with the wage of an African American, and that wage is $15. If the Hispanic's wage was $15, then there would be a chance that the employer would choose either the Hispanic or African American.