Determine the global extreme values of the function f(x, y) = 2x³ – 4y, 0< x, y < 1 fmin fmax

A population of 200 healthy men was followed up for the development of prostate cancer. 10 men were followed-up for 1 year and were then lost to follow-up. After being followed-up for 5 years, 10 men developed prostate cancer. The remaining men who never developed prostate cancer were followed for 10 years. Calculate the total number of person years of observation accrued by this population