Imagine the average time to complete a 4year bachelor degree

Imagine the average time to complete a 4-year bachelor degree is actually 4.7 years based on national data. You collect data on the 68 psychology students who started school during the same semester as you, finding an average time to complete at 4.3 years with a standard deviation of 0.6 years. What would be the effect size associated with a single-sample t test?