The labor force participation rate is defined as the ratio of labor force to the working age population, multiplied by 100. Mathematically,
labor force participation rate = 100 x (labor force/working age population)
In the given question, the working age population is 75 million and the labor force participation rate is 85%, thus the labor force size is:
Size of labor force = Labor force participation rate x working age population / 100 = 85 x 75/100 = 63.75 million people.
Thus, the size of the labor force is 63.75 million people.
Of this labor force, 8 million people are unemployed, thus only 55.75 million (= 63.75 - 8) people are employed.
The labor force includes the population that is either employed or in search of employment (even if it is currently unemployed).
Hope this helps.