The labor force of a country is the sum of the working people, whether employed or not, that is, it excludes retirees, children and people who are out of necessity.
The unemployment rate of a country is the percentage of the workforce that is unemployed.
In this case the workforce is 30 million people and the unemployment rate is 5%.
In this way, the number of unemployed is 5/100 x 30,000,000 = 1,500,000 people which is the same of 1,5 million people.
The fourth answer is correct (D).