I have no idea how to form R code for 3a.

Let (X, Y) be a bivariate random variable with density function f(x, y). Given the pdf f(x, y), the population version of Kendall's tau correlation is defined by T = [!{(x-r)(y-y')>0} - I{(x-1)(y-y') 0, sgn (t) = 1= 0, 1