need solution as soon as possible

Question 6 11 marks (a) Check whether the function fri,Ya(31, 42) = 291 - 192, 0 S y1 S 2, |92| $ 1- [1 - 31| otherwise is a valid probability density function. (b) Consider the probability density function 191 $ 109 fZ1,Z2 (21, 22) = 0