help! Probability statistics

probability statistics question:

1. A certain college gives aptitude tests in the sciences and the humanities to all entering freshmen. If X and Y are, respectively, the proportions of correct answers a student gets on the tests in the two subjects, the joint probability distribution of these random variables can be approximated with the joint probability density.



f(x,y)=2/5 * (2 x+ 3 y) for 0 < x < 1, 0 < y < 1
f(x,y)=0 elsewhere

What are the probabilities that a student will get
(a) Less than 0.40 on both tests; (b) More than 0.80 on the science test and less than 0.50 on the humanities test?