4. Generate a 1000 x 5 matrix of Unif(2,8) random numbers. (a) Let U be your matrix and let ui, i 1,...,5, be the columns of U. Compute the sample means and variances of ui's using the function apply(). What are the two numbers they estimate? Explain. Round your answers to two decimal places using the function round(). (b) Recompute the sample variances of u;'s using the apply() function twice and the sweep() function once in a single line of command as we did in class. Check if the variances agree with those from part (a)