The given bar graph shows the percentage of U.S. women in the labor force from 1960 through 2010. The function f left parenthesis x right parenthesis equals 3.5 square root of x plus 38 models the percentage of U.S. women in the labor force, f left parenthesis x right parenthesis , x years after 1960. Use this formula to solve the following questions.

US women in Labor Force

According to the model, when will 70% of the U.S. women participate in the work force? Show all work and explain your answer in the context of the problem.